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

摘要

The roles of the interferon-γ (IFN-γ) and interleukin-12 (IL-12) produced during natural killer (NK) cell interaction with macrophages (Mφ) were investigated as the basis for the induction of immunoglobulin G2a (IgG2a) anti-bovine serum albumin (BSA) responses by high molecular weight dextran conjugated to BSA (HMW-DEX–BSA). BALB/c mice immunized with HMW-DEX–BSA 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 were higher in mice immunized with BSA conjugated to dextran of molecular weight (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 inhibited when free BSA was added to the HMW-DEX–BSA conjugate. NK cell depletion during HMW-DEX–BSA immunization of mice resulted in significantly lower anti-BSA IgG2a levels without affecting anti-BSA IgG1 levels. Naive splenocytes or Mφ + NK cell co-cultures incubated with HMW-DEX or HMW-DEX–BSA produced higher IFN-γ levels than splenocytes or co-cultures incubated with BSA alone. HMW-DEX stimulated both IFN-γ and IL-12 production by Mφ + NK cell co-cultures in a dose-dependent manner. DEX-induced IFN-γ production by NK cells was dependent upon the presence of IL-12, and IL-12 production by Mφ was dependent upon the presence of IFN-γ in these co-cultures. Both Mφ and NK cells bound DEX to their surfaces. These data 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 Mφ that supports a NK cell/IFN-γ-dependent mechanism for enhancement of anti-BSA IgG2a antibody responses in mice immunized with HMW-DEX–BSA protein conjugates.