On the role of T lymphocytes in stimulation of humoral immunity induced by peptidoglycan-monomer linked with zinc.

Effects of peptidoglycan linked with zinc (PGM-Zn) were investigated on plaque-forming cell (PFC) generation to sheep red blood cell (SRBC) and SRBC-unrelated antibody production in primary and secondary immune response in mice depleted in vivo of CD4+ and/or CD8+ T lymphocytes. PGM-Zn in nondepleted mice stimulated the PFC generation and IgM or IgG and IgG1 production in primary and secondary reaction. Single depletion of CD4 or CD8+ T cells did not change this ability. The effects of PGM-Zn after CD8+ depletion were even greater than those in nondepleted mice. Depletion of both T cell subsets, however, completely abrogated immunostimulatory effects of PGM on PFC generation (primary and secondary response), as well as on primary SRBC-unrelated antibody production, leaving only the increase of IgG in secondary response unchanged. Immunostimulatory effects and isotype switching to IgG1 and IgG2a correlated with the changes in splenic CD4+, CD8+, CD5+ cells, pointing to the regulatory role of these cells and/or their cytokines in PGM-Zn-induced immunostimulation. Altogether the data suggest that PGM-Zn may potentiate the costimulatory signals coming from activated T cells and act on B cells without the T cell help.