Development of Cold Agglutinins in Atypical Pneumonia

IN addition to the classical iso-agglutinins that delineate the four primary blood groups of man, there exist in many normal sera other substances which may cause clumping of erythrocytes and are called `cold' agglutinins because in most instances their action appears at low temperatures only. Specific cold agglutinins, concerned with the sub-groups of type A blood, have been distinguished¹. The cold agglutinins are, however, otherwise considered to be non-specific inasmuch as they will produce clumping of all human red blood cells irrespective of group. Moreover, since they likewise affect the cells of the individual in whose serum they appear, they are sometimes named auto-agglutinins. The reaction is delicate and usually disappears when the serum is diluted beyond 1: 10. Cold agglutinins of this type have attracted attention from time to time when existing in quantity enough to be manifest even at room temperature and so interfere with the crossmatching of bloods for transfusion. Such occasions are still rare enough to warrant reports of single cases of their occurrence. McCombs and McElroy found in the literature thirty-eight instances². Among these were represented diseases as varied as cirrhosis of the liver, trypanosomiasis and pneumonia. With the exception of paroxysmal hæmoglobinuria, which occupies a unique position, there would seem to be no regularity in the behaviour of cold agglutinins in disease, although it may be pointed out that systematic clinical and serological investigation of the subject has been neglected.