T cell activation by anti-CD3 antibodies: function of Fc receptors on B cell blasts, but not resting B cells, and XXXX on the responding T cells.

@entity1 @entity1454 @entity19 @entity6433
Mouse anti-human CD3 (T3) antibodies can induce T cell proliferation in the presence of Fc receptor ( @entity6433 )-bearing accessory cells. Depending on whether the particular antibody can interact with the @entity6433 , it can be mitogenic or otherwise. Previously, some of us (Smith, K. G. C. et al., Eur. J. Immunol. 1986. 16:478) examined @entity1 T cell responses to the murine anti-CD3 antibody switch variants UCHT1 (IgG1) and UCHT1B (IgG2b). Using a novel xenogeneic system with @entity19 macrophages (M phi) and an anti- @entity6433 antibody, 2.4G2, we obtained direct evidence for accessory function of @entity6433 in these responses. However, @entity19 B cells which also possess @entity6433 were not accessory cells. Here we show that resting B cells do not inhibit anti-CD3 responses in the presence of other accessory cells, and they do not synergize with them. They appear to be inert in these responses but this is not simply because of their radiosensitivity. In contrast, B cell blasts proved to be potent stimulators of responses with UCHT1, UCHT1B and OKT3 (IgG2a). All three responses were inhibited by 2.4G2, whereas we have shown previously that the OKT3 response with M phi was not, in keeping with the known specificities of B cell and M phi @entity6433 . These findings are discussed in relation to the molecular cloning of @entity6433 , and we consider the possibility that distinct @entity6433 could be expressed on resting and activated B cells. A report that anti- @entity1454 ( @entity1454 ) antibodies blocked the UCHT1 response with @entity1 monocytes raised the possibility that this molecule might also be involved in accessory function. However, we show that this inhibition is in fact at the level of the T cell, since anti-human, but not anti-mouse @entity1454 antibodies, inhibited proliferative responses and clustering with both @entity1 and @entity19 accessory cells. Our results demonstrate that the principal contribution of accessory cells to anti-CD3 responses may be the provision of an @entity6433 , and that @entity1454 is most probably required at the level of the T cell.
