Immunologic and physicochemical properties of enhancing soluble factors for IgG and IgE antibody responses.

Rabbits were immunized with dinitrophenyl-coupled Ascaris antigen (DNP-Asc) or ragweed antigen (DNP-Rag) included in aluminum hydroxide gel and their mesenteric lymph node cells were cultured for 24 hr in vitro in the presence of free homologous carrier. The cell-free supernatant thus obtained enhanced both IgG and IgE antihapten antibody responses of DNP-primed cells to DNP-heterologous carrier conjugate (DNP-keyhole limpet hemocyanin). Since the cell-free supernatant obtained from Rag-specific cells enhanced antibody response of hapten-primed cells raised by immunization with DNP-Asc, no carrier specificity was involved in the enhancement. It was found that treatment of primed cells with 10-5 M pactamycin suppressed the formation of the enhancing soluble factor, whereas the factor was readily formed in the presence of 2 mug/mol of cytosine arabinoside in the culture. The results indicated that cell proliferation was not required but de novo synthesis of protein was essential for the formation of soluble factor(s). The enhancing factor was not absorbed by either carrier-coated or anti-carrier antibody-coated immunosorbent. It was also found that the enhancing factor was formed by incubating primed cells with carrier-coated Sepharose. The cell-free supernatant containing no free carrier enhanced both IgG and IgE anti-hapten antibody responses. The activities of the cell-free supernatant to enhance IgG and IgE antibody responses were not absorbed by anti-Fab, anti-gamma-or anti-mu-chain antibody immunosorbent, indicating that the nonspecific enhancing factor did not possess immunoglobulin determinant. The cell-free supernatant was fractionated by sucrose density gradient ultracentrifugation and by gel filtration with three radiolabeled proteins, i.e., IgG, ovalbumin, and cytochrome C as markers. Enhancing activity for IgG antibody response was recovered in a fraction between ovalbumin peak (40,000 m.w.) and cytochrome C peak (20,000 m.w.). The activity for IgE antibody response was recovered in a fraction containing IgG marker (150,000 m.w.). By block electrophoresis, both activities were detected in beta globulin fraction. The results suggested that different T cell factors are involved in the IgG and IgE antibody responses.