CHAPTER V
PHYSIOLOGY AND PATHOLOGY OF BLOOD GROUPS
In the foregoing chapter the reactions between the blood groups and the morbid symptoms which may follow the injection of incompatible blood have been described. In the present chapter some account will be given of the more general physiology and pathology of the groups.
It seems to be clear that iso-agglutinins and iso-hæmolysins, that is to say, serum reactions among the individuals of a species, are to be found distributed widely through the animal kingdom. The phenomenon is, however, weak in operation compared with that found among human beings, and it is very much more difficult to demonstrate. The facts have not been investigated for very many species of animals.
Some of the earliest attempts to investigate the distribution of iso-agglutinins among animals were made by Hektoen in 1907. He tested the blood of rabbits, guinea-pigs, dogs, horses, and cattle; his results were negative in every case, but probably his technique was imperfect or an insufficient number of animals was tested. Grouping has been found among goats by Ehrlich. Ottenberg and others believe that they have demonstrated the existence of three groups among steers, and of four groups among rabbits. Von Dungern has shown that there are four groups among dogs. Agglutination reactions were found by Ingebrigtsen and by Ottenberg among cats, but they were not constant, and it was not found possible to distinguish any grouping. The same was found to be true of rats. I have not been able to discover any record of research upon iso-agglutinins in birds or reptiles. The phenomenon of blood groups has a possible bearing on the success or failure of experimental transplantations of tissue, whether healthy or diseased, from one animal to another of the same species. From this point of view an investigation of the blood reactions among mice was carried out by B. R. G. Russell in the laboratories of the Imperial Cancer Research Fund, but he was unable to find any sort of grouping. Ingebrigtsen has made an attempt to correlate the results of the transplantation of arteries in cats with their serum reactions, but he was unable to do so. His results were equally bad whether iso-agglutinins were present or not. Nevertheless, it is highly probable that the success of tissue transplantation in man will be found to be largely dependent upon compatibility of blood groups in donor and recipient. The problem is one that cannot easily be investigated by experiment on animals, among which natural incompatibility is evidently much less well marked than it is in man. A method of overcoming this unsuitability is suggested by the experiments of Ottenberg and Thalimer. These observers, as already mentioned, found that in cats iso-agglutinins were present, though inconstant; on the other hand, iso-hæmolysins were seldom if ever found in normal cats, though they often appeared in the recipients of transfusions. Grafting experiments might therefore be preceded by transfusions designed to stimulate artificially incompatibility of the tissue fluids.
The incompatibility of blood is essentially a phenomenon which distinguishes different _species_ of animals, since in no case can the blood of one species circulate unaltered in the blood-vessels of another kind of animal. This serological specificity may be in some way related to the sterility of one kind of animal with another, though not actually causing it, and so be merely an incidental phenomenon. It cannot be in any sense protective, since it never happens in the course of nature that blood is transferred from one animal to another. In the same way it is difficult to see how there can be any biological “purpose” in similar differences between individuals of the same species, and, so far as is at present known, the possession of a particular group does not confer upon its owner any advantage over the individuals of other groups, such as a relatively greater immunity from disease, longevity, or fertility. It is quite clear that there is no connexion between incompatible blood groups and sterility between individuals.
An investigation of a possible relation between blood groups and disease has been begun by W. Alexander at St. Andrews University. In a preliminary communication concerning the blood groups found among fifty patients suffering from “malignant disease” of all forms, including leukæmia, he has found that there is a considerably higher proportion of Groups I and III than among healthy people. On the other hand, the groups are found in the normal proportions among people suffering from tuberculosis, syphilis, and tetanus. It would, however, be premature to assume that individuals of Groups I and III are more liable to suffer from “malignant disease” than other people, as the numbers tested are, at present, too small for definite conclusions to be formulated. Also it remains to be proved that the presence of malignant disease does not produce an alteration in the agglutinating reactions by which the groups are determined.
It seems probable that the differences between the groups have arisen incidentally in the evolution of mankind, possibly as the result of the parallel descent of two or more original stocks from different sources, which afterwards converged and mingled, with the production of serological hybrids. In view of this it is of interest to find that some investigation of the racial incidence of blood groups has already been carried out. On the Macedonian front during the war a large number of men of many different races were gathered together, and scientific advantage of this opportunity was taken by L. and H. Hirschfeld. The blood groups were determined in approximately 8,000 individuals, including French, English, Italians, Germans, Austrians, Serbs, Greeks, Bulgarians, Arabs, Turks, Russians, Jews, Malagasies, Senegal Negroes, Annamese, and Indians. According to the results obtained by the Hirschfelds, the groups designated II and III show a definite variation in their distribution among different races. As will be seen hereafter, Group I is compounded of the two factors producing Groups II and III, while Group IV results from their absence. It is therefore necessary only to consider the incidence of Groups II and III in calculating the racial differences. For the statistical tables and diagrams the reader must be referred to the original paper published in 1919, but the results may be roughly summarized as follows. It was found that the factor producing Group II is prevalent among European peoples, whereas the factor producing Group III is characteristic of men from Asia and Africa. Thus the Group II factor was found in not less than 45 per cent. among most European peoples. It gradually diminishes in the countries lying between Asia and Central Europe, being present in Arabs 37 per cent., in Russians 37 per cent., in Jews 38 per cent. In Asiatics and Africans it falls considerably, being in Malagasies 30 per cent., in Negroes 27 per cent., in Annamese 29 per cent., in Indians 27 per cent. On the other hand, the factor producing Group III shows exactly the opposite variation. Among the English, the most Western people of Europe, it is rare, being found by these observers to be present in only 10 per cent.; it rises to 14 per cent. in French and Italians, to 18 per cent. in German Austrians, and to 20 per cent. in the Balkan peoples. In Africa and Asia the Group III factor rises considerably, being present in Malagasies 28 per cent., in Negroes 34 per cent., in Annamese 35 per cent., and in Indians 49 per cent.
We may still be far from elucidating the anthropological meaning of these facts, for the mingling of the hypothetical stocks of which mankind is made no doubt began in a remote antiquity, and it is possible that a serologically pure race does not exist. The investigation, however, of the more isolated peoples might throw much light on the problems of anthropology.
Interesting as the wider questions may be, we are here more immediately concerned with the distribution of the blood groups amongst our own population. The percentages in which the four groups occur have been estimated by various observers, and, as will be readily understood from the foregoing remarks, the numbers show some variation. The approximate figures as worked out by three observers in America are as follows:
------+----------+---------------+---------------- | Bernheim | Moss | Culpepper | | (1,600 tests) | (5,000 tests) ------+----------+---------------+---------------- I | 2 | 10 | 3 per cent. II | 40 | 40 | 38 ” ” III | 15 | 7 | 18 ” ” IV | 43 | 43 | 41 ” ” ------+----------+---------------+----------------
The percentages found among the first hundred men whom I tested in the British Army in 1917 conformed almost exactly to the first of these series of figures, and they may be taken as an average result for Western peoples. It will now be seen upon what grounds it was stated in the last chapter that the chances were in favour of the blood of a donor chosen at random being compatible with that of the recipient. If the patient belong to Group II, then 83 per cent. of other bloods will be compatible. If he belong to Group III, 58 per cent. will be compatible. Only if he belong to Group IV will the chance in favour of compatibility fall below 50 per cent.
This statement of the facts concerning distribution of the blood groups will serve to emphasize the absolute necessity for the careful testing of a donor before his blood is used for transfusion. But, further than this, it is necessary to clear away several widely spread misapprehensions as to the group relations between an infant and its mother and between the various members of a family. It has several times been stated in print that a mother’s blood must be compatible with that of her child, or sometimes that a baby has no blood group, so that it may be safely transfused with blood taken from its mother or its father without preliminary testing. On other occasions the statement has been made that the brother or sister of a patient is more likely than other people to belong to the same or a compatible blood group, so that untested blood may be transfused from one member of a family to another with little risk. Knowledge of the existence of blood groups has become somehow mixed up with vague popular beliefs concerning “affinities” and “blood relations.” Such confusions must, however, be dissipated, for none of these statements are more than partially true, and they may lead to a false sense of security and to disaster.
The assertion that an infant has no blood group was tested by the writer some time ago and shown to be false. On several occasions a newly born infant was tested and found to show well-marked agglutination reactions indicating Groups II or III as the case might be. Even in 1905 it had been shown by Martin that reactions could often be demonstrated between an infant’s corpuscles and the maternal serum, and sometimes between the infant’s serum and the maternal corpuscles. More recently (March 1920) the results of a full investigation into the reactions found in infants and children have been published by W. M. Happ in America. These researches began with the testing of blood from the umbilical cord, and this was seldom found to show the blood reactions as given by the adult. So far the statement quoted above was justified. It is even true that the serum of an infant’s blood will usually not give any reaction at birth or during the first month. The percentage in which it does give a reaction increases with the age of the child; after one year it is usually, and after two years always, established. On the other hand, the agglutination reaction in the corpuscles appears before that in the serum, so that the grouping tested in this way may be present immediately after birth, as I found to be the case. It is possible that the grouping which first appears may afterwards be modified, but any change which occurs is always by the addition of factors and not by their subtraction; thus an apparent Group IV may become a Group II or III, or an apparent Group II or III may become a Group I. It is found that when a reaction is present in both the corpuscles and the serum, the group does not afterwards change. Happ’s conclusion, based on his investigations, was that it is unsafe to transfuse an infant with its mother’s blood without first making the usual tests, and the reasons for this will now be evident. In the first place an infant _may_ be possessed of its final blood reactions very shortly after birth, and should therefore be treated in the same way as if it were an adult. In the second place, although its serum may be without agglutinating powers, so that transfused corpuscles will not be attacked, yet its corpuscles may be possessed of pronounced agglutinophilic properties, so that they may be seriously affected by the serum of transfused blood from an incompatible group. In the third place, as will presently be seen, it is by no means the rule that an infant should belong to the same group as its mother, whatever its blood reactions may be.
Another set of observations, leading to precisely the same conclusions, have been made by F. B. Chavasse of Liverpool. He terms the potential agglutination of the fœtal corpuscles by the mother’s serum, and of the maternal corpuscles by the serum of the fœtus, the “maternal threat” and the “fœtal threat” respectively, and states that there is no obvious relationship between the “fœtal threat” and eclampsia or the toxæmias of pregnancy. The inference is therefore justified that there is no transference of the agglutinating substances in either direction across the placental membranes. No chemical “immunity” is acquired, therefore, on either side, since the protection is mechanical. This agrees with the fact observed by Happ that the mother’s milk contains the same agglutinins as the serum of her blood; but these do not have any deleterious effect upon the infant, and are therefore either not absorbed at all or are destroyed in the process of digestion.
The statement that the blood group of an infant is not necessarily the same as that of its mother can be amplified, for it has been found that blood groups are inherited on a definite plan, so that if the groups of the parents be known, certain predictions can be made as to the possible groups that may be found among their offspring. Many characters in animals and plants have been shown during the last twenty years to be transmitted according to the Mendelian plan of inheritance, but up to the present time very few normal characters in man have been isolated, and their manner of inheritance demonstrated, though a number of pathological conditions have been shown to conform to the theory. It is therefore of much interest to find that the inheritance of blood groups in man can be quite satisfactorily and consistently explained in Mendelian terms.
According to this theory, each quality in an organism which can be isolated and investigated independently of other qualities, is termed a “unit character,” and the appearance of each such unit character is determined by the presence of something called a “factor” in the sexual cells or “gametes,” male and female, by the union of which the individual is formed. Further, these unit characters are believed to occur in alternative pairs, and at first it was supposed that each alternative pair consisted of “dominant” and “recessive” characters, the second of which could only make its presence apparent in the individual if the dominant character were absent. Subsequently it was seen that the dominant and recessive characters need not necessarily consist of two positive, though opposite, qualities, but might better be regarded as consisting of the presence of a character and its absence. To use a classical illustration of this view, sweet peas may be classified into tall peas and dwarf peas. At first the unit characters were taken to be tallness (dominant) and dwarfness (recessive). Later this idea was modified, and it was said that potentially all peas are dwarf, but to some is added a factor producing tallness, this factor being absent in those that are dwarf. To represent this idea more simply a conventional notation has been used, according to which the large letters of the alphabet indicate the presence, and the small letters the absence, of each factor.
In order to apply this theory to the case under consideration, it has been suggested that two pairs of factors are concerned:
A the _presence_ of the character producing Group II.
a the _absence_ of the character producing Group II.
B the _presence_ of the character producing Group III.
b the _absence_ of the character producing Group III.
Each pair of factors is transmitted independently of the other. Both A and B may be absent, in which case the individual belongs to Group IV; or both may be present, and in this case the individual gives the reactions of Group I.
It must be understood that the term “character producing Group II” is here used as a convenient way of expressing the obscure and probably complicated set of properties responsible for the reactions manifested by individuals of Group II. It includes not only the agglutinin or hæmolysin of the serum which reacts with corpuscles of Group III, but also the complementary iso-agglutinin or iso-hæmolysin by virtue of which the corpuscles react with serum of Group III.
The appearance of the different groups can now be further explained in terms of the Mendelian theory. According to the conception of the individual formulated by Mendel, each cell of the body contains an ingredient derived from each of the sexual cells or gametes which united at the moment of fertilization of the ovum by the spermatozoon to form the individual. But when the adult in his or her turn forms sexual cells or gametes, these ingredients separate again, half the gametes containing one of the pair of factors, half containing the other. This process certainly takes place during the rearrangement of the nuclear substance or chromosomes at the cell divisions which result in the formation of the ripe sexual cells. It is called the “segregation of the gametes.”
In the present case the unit character producing Group II will be first considered. As already explained, the factors concerned may be called A and a, and the individual of Group II may be constituted by AA or Aa, and the gametes, therefore, may contain either A or a, but not both. The individuals resulting from the union of the gametes derived from Aa adults may then be constituted in three ways--AA, Aa, or aa. Similarly for the unit character producing Group III, the factors concerned may be called B and b, and the individual of this group may contain BB or Bb. The gametes then contain either B or b, and the individual resulting from their union may again be constituted in three ways--BB, Bb, or bb.
In computing the results, however, it must be remembered that most, or perhaps all, people are hybrids, so that both unit characters are present simultaneously, and all the factors must be taken into account. It is easily seen that the gametes derived from a hybrid individual must contain one of the following combinations:
AB, Ab, aB, or ab,
and consequently the individuals formed from them must have one of the following constitutions:
AB--Ab, Ab--aB, aB--ab, ab--ab, AB--AB, AB--aB, Ab--ab, aB--aB, AB--ab, Ab--Ab.
This includes all the possible combinations that can result from the chance union of the gametes, and it is now clear which blood groups result from which combinations, if it be remembered that
A is dominant to a, B ” ” ” b,
and that
Group I results from the _presence_ of both A and B. ” II ” ” ” ” ” A only. ” III ” ” ” ” ” B ” ” IV ” ” ” _absence_ ” both A and B.
Thus Group I may be constituted by AB--AB. AB--aB. AB--Ab. AB--ab. Ab--aB. Group II may be constituted by Ab--Ab. Ab--ab. ” III ” ” ” ” ab--aB. aB--aB. ” IV ” ” ” ” ab--ab.
It now becomes evident what offspring may result from the union of parents who have any of the above constitutions. Thus parents both of Group I may have offspring belonging to any group according to which of the five possible constitutions they possess. If the union be represented by
AB--AB × AB--AB,
then only offspring of Group I can result, since every gamete contains both A and B. The other possibilities may be worked out by the reader if he desire.
Similarly, a union of Groups I × II, I × III, or II × III may produce any of the groups, definite limitations being imposed by the detailed constitution of the parents. On the other hand, the remaining group unions that are possible can only produce a more limited variety of offspring. Thus II × II or II × IV can only produce Groups II or IV; III × III or III × IV can only produce Groups III or IV; IV × IV can only produce Group IV.
The Mendelian theory of inheritance in general has been subjected to a prolonged and widely ramifying series of tests, and it seems in the present state of knowledge to present a satisfactory and consistent explanation of the facts. For a more extended account of it the reader must be referred to the standard works on the subject.[6] As regards its application to the present case, the test of actual experiment has not yet been carried out on a large scale. A series of observations has, however, been published by J. R. Learmonth, who, taking forty families at random, determined the blood groups of both parents and the children in each family. In this way he tested most of the possible group matings, and, with a single exception, the group inheritance conformed to the theory as set out above. Additional confirmation of the truth of the theory is afforded by the pedigree given on the page opposite. I have recently collected this pedigree, which includes fifty-nine individuals belonging to four generations, and it has not been published before. It will give, perhaps, a more graphic representation of the facts than has been conveyed by the brief summary contained in the foregoing pages. It does not show any variation from the results that were to be anticipated according to the theory.
The exceptional result obtained by Learmonth in one of his forty families serves to emphasize the clarity of the theoretical considerations. In this family parents both belonging to Group IV had a child showing the reactions of Group I. There are three possible explanations of this:
(1) The observations were at fault.
(2) The putative father was not the real father.
(3) The Mendelian theory of inheritance is wrong.
The Mendelian theory is established on so firm a basis that, in the absence of more numerous exceptions, (3) may be rejected. There is no reason for supposing that the observations were inaccurate, and we are therefore brought to the conclusion that in such a case the child is illegitimate.
The conclusions which emerge from this structure of theory and fact are obviously of very great clinical importance. It is now clearly demonstrated that a mother belonging, say, to Group I, may give birth to a child belonging to any one of Groups I, II, III, or IV; her blood may not be used for transfusing her child without a grave risk that the “maternal threat” may culminate in the death of the child. The same applies to the possible relations between a father and his child. Two brothers, again, may belong to Groups II and III respectively. Even the blood of twins may be mutually incompatible, except in the rare case of “identical twins,” who, it may be supposed on theoretical grounds, would certainly belong to the same group, though I am not aware of a case in which this has been put to the test. As much care, therefore, must be exercised in testing the blood groups of members of the same family before performing a transfusion as would be taken before using a donor who is not related to the patient.
The medico-legal importance of the facts concerning the inheritance of blood groups is also evident, and, although this test has not yet been used as a test of legitimacy, there can be little doubt but that it will be so used in the near future. The information to be derived from it is of a negative rather than a positive character. Thus the occurrence of Group III blood in a child whose mother is of Group II and putative father of Group I cannot be taken as a proof either of legitimacy or the reverse. But if, as in Learmonth’s case, parents both of Group IV have a child of Group I, or if parents both of Group II have a child of Group I or III, then this may be taken as a proof of illegitimacy.
There is not much experimental evidence concerning the effect of various pathological conditions on the agglutination reactions of the blood and serum. It has already been mentioned that there is no proof that the possession of any particular blood group confers upon its owner any special immunity from, or liability to, disease. The numbers, investigated by Alexander in the communication referred to on p. 81, are too small for the observation to be of much value; it is also necessary, as a preliminary to any such research, to demonstrate that there is no abnormal alteration in the reactions of the blood of these patients. It is probable, indeed, that evidence of this alteration in malignant disease already exists, for a reference to it is to be found in Kolmer’s work on serum-therapy,[7] but I have been unable to find a record of the investigation.
I possess, on the other hand, evidence that an alteration may take place in some other diseases, such as pernicious anæmia and familial, or acholuric, jaundice. Evidence for the former was provided recently by a patient whose condition was typical, clinically, of the last stages of the disease. Her corpuscles, tested with stock sera, belonged to Group II, but her serum, tested directly with the corpuscles of prospective donors known to belong to Group IV, agglutinated these vigorously, so that a transfusion could not safely be performed. The same phenomenon has been found by other observers. In acholuric jaundice there is a progressive destruction of red corpuscles in the patient’s circulation. This appears to be connected in some way with an abnormal functioning of the greatly enlarged spleen, since the destruction of corpuscles ceases almost at once when this organ is removed. There seems to be, in addition, an alteration in the blood reactions. In a case which I tested recently, the patient’s corpuscles were quickly agglutinated by serum of Group III, and he therefore nominally belonged to Group II. His serum, however, when separated and tested against other bloods of known groups gave, in addition to a rapid agglutination of corpuscles belonging to Group III, a definite, though slower, agglutination of corpuscles belonging to Groups II and IV, showing that it had acquired abnormal properties.
It is possible that there are similar alterations of reactions in other pathological conditions. The instances mentioned above suggest that the serum is affected rather than the corpuscles, but further investigations are needed. It is an observed fact that blood outside the body soon develops the property of auto-hæmolysis. If blood is drawn from a vein, put into a test-tube, and allowed to clot, then after twenty-four hours or more the serum which has separated from the clot begins to be tinged with hæmoglobin, even though it has remained absolutely sterile. It appears, therefore, that the serum develops a hæmolysin and the corpuscles the corresponding iso-hæmolysin, the interaction of which results in the breaking up of corpuscles. If this process takes place in normal blood outside the body, it would not be surprising to find that it may also occur abnormally inside the body. This actually happens in the condition known as paroxysmal hæmoglobinuria. The pathology of the disease is obscure, but it seems that a hæmolysin develops in the serum as the result of cooling in the extremities and hæmolysis takes place when the cooled serum is again warmed by being restored to the general circulation. The presence of this hæmolysin in addition to the normal hæmolysins has been demonstrated by Moss. It is possible that a similar though less acute change takes place in acholuric jaundice. Blood transfusion, therefore, is not likely to be efficacious in such conditions, since the transfused corpuscles may be destroyed whatever the apparent blood group of the patient. Some of the facts of auto-hæmolysis have been recently investigated by Bond, but it is not necessary to give the details here. He concludes that the development of auto-hæmolysins, which are non-specific and independent of the specific hæmolysins of the blood groups, has a biological significance in the history of the red corpuscle, and is a product of ageing. The biochemistry, however, of the process remains at present entirely unknown.
The necessity for careful blood grouping in every case before performing a transfusion has now been sufficiently emphasized, but before proceeding to the description of the methods of choosing a donor and of grouping, a possible danger must be mentioned which may arise even when the blood groups are known. In the preceding chapters references were made to the effects which have been observed to follow repeated transfusions given in the treatment of a condition such as pernicious anæmia. In such cases, although the groups were ascertained, and the bloods were also tested directly against one another without any incompatibility being detected, yet when the third or fourth transfusion was given, symptoms of toxæmia followed, sometimes with hæmolysis. The death of the patient has even been hastened in this way. A very striking instance of this phenomenon, which has been recently reported (278), will serve to bring home the reality of the danger. A boy was transfused by the citrate method with blood from his father, and this was followed only by a mild febrile reaction such as is often observed. Eighteen days later a second transfusion with blood from the same donor was performed, and after 150 cc. had been given, a severe reaction resulted, which was followed later by pronounced hæmoglobinuria. In this case the bloods of donor and recipient had been tested against one another directly, but this was not repeated, and the groups were not ascertained until afterwards. Probably there was some error in the original test, for it afterwards appeared that the boy belonged to Group I and his father to Group III, so that there should have been agglutination of the boy’s corpuscles by his father’s serum outside the body. Nevertheless, Group I individuals have been called the “universal recipients,” and no ill effects are usually observed whatever blood be used for transfusing them. In the other cases already mentioned a reaction followed the later transfusions, even when the donor and recipient belonged to the same group. It appears that by repeated transfusions the recipient becomes as it were sensitized to the blood of another individual even of the same group, and consequently great caution must be used in giving the later transfusions of a series. Some light is thrown on this question by the observations of Ottenberg, already referred to, concerning the artificial production of iso-hæmolysins in cats. In these animals iso-agglutinins are found, but iso-hæmolysins seldom or never. The reaction is, however, found to become hæmolytic in the recipients of transfusions, and it is then selective. It seems, therefore, that the group reactions may not be as clearly defined as was at one time supposed. Probably there are slight incompatibilities of an unknown nature between individuals of the same or compatible groups. These are very seldom of any consequence in a first transfusion, but become accentuated as the result of “sensitization,” and in later transfusions have a pronounced influence. This “over-lapping” of groups has been mentioned on another page. It must not be supposed that any untoward results follow repeated transfusions as a general rule, for usually no such effect is observed. In order, however, to minimize the risk, it may be suggested that the following precautions should be taken: (1) The donor should be actually of the same group as the recipient, and not merely of a theoretically compatible group; a patient, for instance, of Group II should receive blood of Group II rather than of Group IV. (2) The same donor should not be used for the later transfusions of a series, on the grounds that the sensitization appears to be an individual rather than a group phenomenon. (3) In performing the later transfusions, the blood should be given at first very slowly, so that it may be discontinued at the first appearance of any signs of a reaction.