Cytolytic activity of Ia-restricted T cell clones and hybridomas: evidence for a cytolytic mechanism independent of interferon-gamma, lymphotoxin, and tumor necrosis factor-alpha.

Ten different helper T cell (Th) hybridomas that are specific to Ia or antigen plus Ia were found to express nonspecific cytolytic activity toward the cytotoxin (CT)-resistant P815 cells upon activation with either Con A or a monoclonal anti-T3 antibody (T3-mAb). In contrast to cytolytic Th1 clones which secrete high levels of interferon-gamma (IFN-gamma) and cytotoxin (CT) (lymphotoxin (LT, also known as TNF-beta) or tumor necrosis factor-alpha (TNF-alpha], these Th hybridomas produce low or undetectable levels of IFN-gamma and CT. No inhibitory activity of IFN-gamma and CT was observed in culture supernatants of activated Th hybridomas. Double-chamber experiments demonstrated that CT-sensitive L929 cells when physically separated from activated Th1 clones were killed by membrane-permeable CT. Under identical experimental conditions, lysis of P815 cells did not occur. Moreover, activation of Th hybridomas directly in wells containing the CT-sensitive L929 cells failed to induce target cell lysis. This confirms that these Th hybridomas produce little CT and argues against high local concentrations of CT being responsible for Th hybridoma-mediated killing of P815 cells. Finally, a polyclonal rabbit antiserum to rTNF-alpha, which strongly and specifically inhibited CT-mediated and Th1 clone-mediated killing of L929 cells, failed to inhibit P815 lysis by activated Th1 clones and Th hybridomas. These observations establish that a cytolytic mechanism independent of IFN-gamma, LT, and TNF-alpha is responsible for lysis of CT-resistant target cells.

Agglutination and phagocytosis of pneumococci by immunoglobulin G antibodies of restricted heterogeneity.

Sera from rabbits that were hyperimmune to type 3 or type 8 pneumococcal capsular polysaccharide were fractionated by starch block electrophoresis, and fractions containing large quantities of anticapsular IgG of restricted molecular heterogeneity were evaluated for their ability to agglutinate and opsonize encapsulated pneumococci. Specific anticapsular IgG was readily absorbed by the organisms. Each CFU of type 3 organisms was capable of absorbing 5 X 10(7) molecules of IgG, and the type 8 organisms absorbed 5 X 10(6) molecules/CFU. Only small amounts of nonimmune IgG were absorbed. Agglutination occurred only after 10(6) molecules/CFU IgG had been absorbed by type 3 organisms, and 10(4) to 10(5) molecules/CFU had been absorbed by type 8 organisms. After larger quantities of IgG had been absorbed, a prozone phenomenon was apparent. Anticapsular IgG in the absence of complement did not promote phagocytosis by human or rabbit PMNs below levels that caused agglutination. In the presence of complement, only about one tenth as much IgG was necessary to promote phagocytosis. Thus these encapsulated pneumococci can absorb large quantities of specific rabbit IgG antibody of restricted heterogeneity. In the presence of complement, approximately 1% of the antibody that can be absorbed by the organisms will promote phagocytosis. In the absence of complement, approximately 10% of the antibody that can be absorbed is required for agglutination or phagocytosis.