The role of the Fc receptor (FcR) of thymus‐derived lymphocytes II. Presence of FcR on suppressor cells and direct involvement in suppression

Abstract

Abstract Alloantigen‐activated T cells (ATC) were prepared by injecting C3H/He thymocytes into host‐irradiated BALB/c mice. ATC were taken from the spleen of the recipients at day 5 and tested for their activity on “In vitro” primary antibody production to sheep red blood cells (SRBC) induced in splenic C3H/He lymphocytes. ATC added 24 h after antigen were found to be suppressive. Separation of ATC by velocity sedimentation, according to cell size showed that suppressor cells were found in each population, medium and large lymphocytes, however, being more active. Separation of ATC, according to the presence of Fc receptor (FcR) at their membrane was achieved by velocity sedimentation after rosetting with IgG‐sensitized SRBC (EA). Suppressor cells were then found in FcR + and not in FcR − fractions, the degree of suppression being parallel to the ratio of FcR + cells. At both extremes, pure populations of FcR + cells were highly suppressive, while populations of ATC, completely devoid of FcR + cells, were inactive. Since FcR is a very labile molecule at the T cell surface and shed within 3 h at 37°C, but not at 4°C, ATC were pre‐incubated at each temperature and added 24 h after antigen to the spleen cell cultures. In these cases, ATC having released their FcR, were much less suppressive than control ATC, and in previous work we have shown that the suppressive activity was found in the cell supernatant associated with an FcR‐like molecule (immunoglobulin‐binding factor). The data therefore allow the conclusion that FcR may be a marker of nonantigen‐specific suppressor T cells and seems to be involved itself in the suppression phenomenon.