A low level of macrophages enhances anti-TNP plaque-forming cell generation by human lymphocytes against TNP-Brucella abortus, a T-independent antigen.

Making use of trinitrophenyl-Brucella abortus (TNP-Ba), a T-independent antigen, the mechanism of antibody production in vitro by human lymphocytes was studied, focusing on the accessory role played by macrophages (m phi). Human tonsillar cells and peripheral blood lymphocytes (PBL), and their fractions which were depleted of T cells, M phi, or both by rosetting with sheep erythrocytes and glass adherence plus passage through a Sephadex G-10 column, were stimulated in vitro with TNP-Ba under optimal culture conditions. Substantial antibody response against the antigen was induced in the whole tonsillar cells, while no appreciable level of response was induced in the whole PBL. The level of response observed after T-cell depletion was not different from that of the whole cells. In contrast, the response was significantly enhanced both in tonsillar cells and in PBL by depleting M phi to a low level, such as 1-2% of the cultured cells. It was further shown that a small amount of M phi added back to the M phi-depleted fraction activity suppressed the response again to the level seen in the whole cells. If allogenic M phi were substituted for autologous ones, the same degree of suppressor function was observed irrespective of the difference seen in the HLA types.