Genetic difference in the proliferative response to T mitogens between Hi/PHA and Lo/PHA lymphocytes is independent of accessory cell function.

The role of the macrophage as accessory cell in the proliferative response of lymphocytes to phytohemagglutinin (PHA) was studied in two lines of mice genetically selected for high and low responsiveness to T mitogens. Adherent cell depletion of lymph node cells abrogated the low (Lo)/PHA response, but only partially inhibited the high (Hi)/PHA response. Addition of peritoneal cells provided either by Hi/PHA or by Lo/PHA mice equally restored Hi/PHA responsiveness but had only a slight reconstituting effect on the inhibited Lo/PHA response. Equivalent enhancement or suppression of proliferation of untreated lymph node cells was obtained by the addition of increasing percentages of each of the two peritoneal cell populations. However, the maximum level of the Lo/PHA response never reached that of Hi/PHA cells. These data indicate that the bidirectional selective breeding has not modified the potentialities of the macrophages as accessory cells but has resulted in an impaired response of Lo/PHA lymphocytes to the signals delivered either by accessory cells or by T mitogens.