In vitro demonstration of two antigenically-distinct rabbit lymphocyte populations

Two populations of lymphocytes have been demonstrated in the rabbit by using a goat antiserum directed to rabbit thymus cells. When incubated with rabbit lymphocytes from peripheral blood the IgG fraction of this antiserum (ATG) completely suppressed lymphocyte transformation initiated by phytohemagglutinin (PHA) or concanavalin A (Con A) but did not affect stimulation by goat anti-rabbit Fab. Neither preimmune IgG nor ATG absorbed with thymus or lymph node cells was capable of affecting transformation. The method of purification of ATG and studies involving order of addition, the effect on human lymphocytes and the effect of the F(ab′)2 and Fab′ fragments of ATG indicate that the primary mechanism of action of ATG is not to prevent the binding to the lymphocyte of Con A or PHA. ATG but not preimmune IgG appeared to be lymphocytotoxic under conditions similar to those used for transformation experiments. The most straightforward interpretation of these data is that ATG in vitro selectively eliminates the population of lymphocytes susceptible to stimulation by Con A and PHA but does not affect lymphocytes carrying immunoglobulin determinants. Thus thymus-derived cells have on their surface receptors for ATG, PHA and Con A while the other lymphocyte population expresses receptors for immunoglobulin.