Natural killer cell-dependent immunoglobulin G2a anti-bovine serum albumin(BSA) response elicited by high molecular weight dextran-BSA conjugates associated with dextran-mediated macrophage-natural killer cell interaction

The roles of the interferon-gamma (IFN-gamma) and interleukin-12 (IL-12) pr oduced during natural killer (NK) cell interaction with macrophages (M phi) were investigated as the basis for the induction of immunoglobulin G2a (IE G2a) anti-bovine serum albumin (BSA) responses by high molecular weight dex tran conjugated to BSA (HMW-DEX-BSA). BALB/c mice immunized with HMW-DEX-BS A produced significantly higher levels of both IgG1 and IgG2a anti-BSA than did mice immunized with BSA alone. Both IgG1 and IgG2a anti-BSA levels wer e higher in mice immunized with BSA conjugated to dextran of molecular weig ht (MW) 5 000 000-40 000 000 compared with dextran of MW 10 000-60 000. The enhancement of anti-BSA IgG2a levels but not of anti-BSA IgG1 levels was i nhibited when free BSA was added to the HMW-DEX-BSA conjugate. NK cell depl etion during HMW-DEX-BSA immunization of mice resulted in significantly low er anti-BSA IgG2a levels without affecting anti-BSA IgG1 levels. Naive sple nocytes or M phi + NK cell co-cultures incubated with HMW-DEX or HMW-DEX-BS A produced higher IFN-gamma levels than splenocytes or co-cultures incubate d with BSA alone. HMW-DEX stimulated both IFN-gamma and IL-12 production by M phi +NK cell co-cultures in a dose-dependent manner. DEX-induced IFN-gam ma production by NK cells was dependent upon the presence of IL-12, and IL- 12 production by M phi was dependent upon the presence of IFN-gamma in thes e co-cultures. Both M phi and NK cells bound DEX to their surfaces. These d ata demonstrate that BSA linked to HMW-DEX enhanced both T-helper-1- and T- helper-2-associated antibody responses to BSA. The results also indicate an IL-12-dependent positive feedback interaction between NK cells and M phi t hat supports a NK cell/IFN-gamma -dependent mechanism for enhancement of an ti-BSA IgG2a antibody responses in mice immunized with HMW-DEX-BSA protein conjugates.