Studies on Immunosuppression by Cobra Venom Factor

Abstract

CVF administered before immunization can profoundly depress humoral responses in C-sufficient mice. In AKR/J C5- mice given CVF before i.v. immunization with SRBC, only IgG levels were depressed, IgM titers being equivalent to those of untreated controls. The immunosuppressive effect became inapparent when the i.p. route of immunization was adopted. In DBA/2J C5- mice reduction of both IgG and IgM titers was observed irrespective of the route of immunization. The degree of suppression was, however, much more marked when mice were challenged intravenously. Essentially identical results were obtained with C5+ DBA/1J mice. These studies indicate that immunosuppression by CVF is unrelated to activation of the late C components. The significance of these findings is discussed with reference to the possibility that the generation of biologically active C fragments in conjunction with a C3 deficiency may account for immunosuppression by CVF.

Endogenous complement-activating IgM is not required for primary antibody responses but promotes plasma cell differentiation and secondary antibody responses to a large particulate antigen in mice

“…Because the phenotype in animals lacking any of these components is similar, it is assumed that the major role of C1q, C2, C3, and C4 in antibody responses is to generate the C3 split products constituting ligands for CR1/CR2. Mice lacking component C5 of the terminal pathway ( 14 ), or factor B of the alternative pathway ( 15 , 16 ), have normal antibody responses whereas mice deficient in mannan-binding lectin (MBL) of the lectin pathway may exhibit normal, moderately lower or moderately higher antibody responses ( 17 – 20 ). Importantly, the reduced antibody response in MBL-deficient mice is never as strong as that seen in C1q-deficient mice ( 3 , 4 ).…”