Antigen‐specific suppression of anti‐influenza antibody production in man. Possible role of a membrane‐antigen complex

Abstract

E rosette-forming (E+) cells from human secondary lymphoid tissue were incubated with high dose influenza A virus (Mem-Bel) in an attempt to generate suppressor T cells. Suppression was assayed by transferring the antigen-pulsed E+ cells into effector cultures consisting of E+ and E- cells stimulated with immunogenic amounts of either the inducing virus Mem-Bel) or the non-cross-reacting influenza B virus (B/HK). The transfer resulted in marked inhibition of IgG, IgA and IgM antibody production to Mem-Bel but not to the control antigen, B/HK virus. The suppressive effect was specific at the level of induction as well as expression since E+ cells exposed to high dose Mem-Bel could provide help to an effector culture containing E- cells and optimal dose of B/HK virus. However, metabolically active cells did not appear to be required for suppression. Thus, it could be elicited (a) after only 15 min incubation of E+ cells with high-dose virus and (b) by E+ cells exposed to irradiation, incubated in the presence of metabolic inhibitors, or disrupted by repeated freeze thawing. In contrast, treatment of E+ cells with pronase reversed the suppressive effect. Interestingly, virus heated to 70 degree C failed to induced suppression, while retailing the ability to elicit a normal helper response. Suppression induced by exposure to standard amounts of high-dose antigen was mediated by T cells of both helper/inducer (Leu-3a+) and suppressor/cytotoxic subsets (Leu-2a+), but not by B cells. Two groups of observations pointed to the B cell as the target of suppression. First, suppression could still be transferred to effector cultures in which helper T cells had been replaced by T cell-replacing factor or suppressor T cells removed by irradiation. Second, significant inhibition of antibody production was obtained when the transfer of antigen-pulsed E+ cells was delayed for up to 120 h after initiation of the effector culture. Taken together the results suggest that suppression in this system is due to the formation of an antigen bridge between specific receptor sites on the T cell membrane and the target. Although not dependent on triggering of metabolically active suppressor T cells the phenomenon highlights the need for care in interpreting the mechanism of suppression by high-dose antigen and could, in addition, represent a biologically important control mechanism capable of rapid inhibition of effector T cells and B cells in sites of high antigen concentration.

High Dose Suppression of Human Anti‐Influenza A Virus Responses Using T Cell Clones

“…High dose suppression by E ^ cells was shown previously to occur after exposure to influenza virus for as short a time as 15 min (3). When taken in conjunction with the findings here that the virus did not bind to T cell clones via antigen specific receptors (Table 3), the suppressor effect was unlikely to require proliferation of the antigen-coated T cells.…”

“…Nevertheless, it is an interesting phenomenon for two reasons. First, it highlights the importance, particularly in in vitro systems, of formally demonstrating the need for viable cells, evidence for which is frequently lacking in published papers on suppression (3). This criticism may also apply to experiments purporting to show the existence of discrete helper and suppressor determinants on both influenza A virus HA (11) and other antigens such as hen egg lysozyme (12).…”

“…Ten nanograms of antigen were added to each culture and they were incubated for 6 days in a humidified incubator at 37" in 5% CO2 in air. Cells were then washed and recuttured for a further 24 h in 0 5 ml RPMI in 5% foetal calf serum (FCS) as described previously (3). The effector cultures were performed in triplicate and results expressed as mean ± SD.…”

“…Major histocompatibility complex. production on transfer to an effector culture in an apparently antigen-specific manner (3). However, metabolically active T cells were not required and both CD4 (T helper) and CD8 (T suppressor/cyiotoxic) subsets were equally effective in transferring suppression.…”

Antigen‐specific suppression of human antibody responses by allogeneic T cells II. Cell interactions involved in the generation of suppression

“…We have recently argued, however, that suppression described in these in vitro systems may not be specific at the effector level [33], even when T, cells are induced by antigen [34], and it is possible that the apparent requirement for T, inducer cells may be restricted to nonspecific suppression as reported in the mouse [29]. The role of antigen-specific T, cells in the regulation of antibody responses in man is even further complicated by recent work showing that antigen-specific suppression by E' cells incubated with high (tolerogenic) doses of antigen does not require viable T cells, and is likely to be mediated by an antigen-T cell membrane complex acting directly at the B cell surface rather than by metabolically active T, cells [35]. The possibility that antigen and polyclonal mitogens activate distinct subsets of B cells subject to different immunoregulatory mechanisms should also be considered, in which case an understanding of the relationship between antigen-specific and nonspecific suppression in man may depend on identifying B cell subsets equivalent to murine Lyb 5' and Lyb 5-B cells.…”