In vivo depletion of macrophages by desulfated iota-carrageenan in mice.

Almost 90% of the sulfate groups of iota-carrageenan (CGN) was removed with acid-methanol in an attempt to obtain a product which would selectively eliminate macrophages in mice. Desulfated CGN(DS-CGN) failed to induce in vivo polyclonal antibody production in DBA/2 mice. However, the number of phagocytes in the peritoneal cavity, spleen, thymus and lymph node of DBA/2 mice was reduced stringently by DS-CGN treatment. The number of Mac-1 positive cells(macrophages) in DS-CGN-treated mice gradually decreased for at least 7 days after the last injection of DS-CGN. In contrast, the relative proportion of T and B lymphocytes in the lymphoid organs was unaffected by DS-CGN treatment. DS-CGN suppressed antibody responses to SRBC, a T cell and macrophage-dependent antigen, but no such suppressive effect was observed in the polyclonal antibody responses to LPS, a T cell and macrophage-independent B cell activator. Furthermore, the impaired SRBC antibody responses in DS-CGN-treated mice were restored following transfer of adherent cells but not T cells. These experimental results indicate that DS-CGN selectively eliminates macrophages without influencing lymphocyte function in vivo.