An intracellular self protein synthesized in macrophages is presented but fails to induce tolerance.

Mice deficient for the fifth component of murine complement (C5), unlike normal mice, do not possess the secreted form of C5 in their body fluids and can be readily immunized to serum-derived normal C5. Although macrophages from C5-deficient mice do not secrete C5, they synthesize the precursor form (pro-C5). Therefore contact of T cells with autologous pro-C5 presented by macrophages is theoretically possible. We show that macrophages from C5-deficient mice can Indeed stimulate a class II restricted CS-specific T cell clone without addttion of exogenous C5. lmmunization of C5-deficient mice with autologous pro-C5 induces vigorous C5-specific T cell proliferation and pro-C5 is recognized by C5-specific T cells in , demonstrating that this protein fails to induce tolerance under physiological condltions. Thus, intraceliuiar pro-C5 is processed and presented by C5-deficient macrophages and can activate T cell clones , yet is neither immunogenic nor tolerogenic for T cells in . [ABSTRACT FROM PUBLISHER]