High molecular weight dextran-peptide conjugate enhancement of peptide specific antibody: Dependence upon macrophage regulated natural killer cell production of interferon gamma

In vivo studies were performed to determine the immunomodulatory effects of high molecular weight dextran (HMW-DEX) conjugated to bovine serum albumin (BSA) and to study the role of natural killer (NK) cells in enhancing anti-BSA antibody responses to HMW-DEX-BSA conjugates in mice. In vitro studies were conducted to investigate the regulatory effects of macrophages {dollar}rm (mphi ){dollar} on dextran induced NK cell interferon gamma {dollar}rm (IFNgamma ){dollar} production. In the in vivo studies BSA was covalently linked to the thymus independent type-2 antigen (TI-2-Ag) {dollar}alpha (1to 6){dollar} dextran of high molecular weight {dollar}(5{lcub}-{rcub}40times 10sp6{dollar} daltons) and low molecular weight (LMW) {dollar}(10{lcub}-{rcub}60times 10sp3{dollar} daltons). These studies were conducted by immunizing mice with HMW-DEX-BSA, LMW-DEX-BSA or BSA. Results showed that both IgG1 and IgG2a anti-BSA levels significantly elevated in mice immunized with HMW-DEX-BSA conjugate compared to mice immunized with BSA or LMW-DEX-BSA. This enhanced response was achieved by amounts of conjugated protein as low as 2 {dollar}rmmu g.{dollar} Dextran molecular size was found to be critical in this response in that both IgG1 and IgG2a anti-BSA levels were higher in mice when the conjugate contained HMW-dextran compared to LMW-dextran. The enhancement of anti-BSA IgG2a but not anti-BSA IgG1 levels was inhibited when BSA was added to the HMW-DEX-BSA conjugate. NK cells depletion of HMW-DEX-BSA immunized mice resulted in significantly lower anti-BSA IgG2a levels without affecting anti-BSA IgG1 levels. When NK cell depletion was discontinued and an another boost of BSA given, anti-BSA IgG2a levels were restored. In vitro cytokine analyses data show that when naive splenocytes or {dollar}rm mphi{dollar} and interleukin-2 (IL-2) activated NK cell {dollar}rm (mphi+NK){dollar} co-cultures incubated with HMW-DEX, HMW-DEX-BSA, LMW-DEX-BSA, or BSA, {dollar}rm IFNgamma{dollar} levels were elevated as early as day 2 in HMW-DEX-BSA and dextran stimulated cultures compared to BSA stimulated cultures.; In the second study in vitro experiments were performed to test the {dollar}rm mphi{dollar} regulation of dextran induced interferon gamma {dollar}rm (IFNgamma ){dollar} production by NK cells. The results demonstrated that HMW-DEX stimulated both {dollar}rm IFNgamma{dollar} and IL-12 production by {dollar}rm mphi +NK{dollar} co-cultures in a dose dependent manner. The molecular size of dextran was important in this effect in that HMW-DEX induced higher levels of IL-12 and {dollar}rm IFNgamma{dollar} than LMW-DEX. DEX induced {dollar}rm IFNgamma{dollar} production by NK cells was dependent upon the presence of IL-12, and IL-12 production by {dollar}rm mphi{dollar} was dependent upon the presence of {dollar}rm IFNgamma{dollar} in these co-cultures. When {dollar}rm mphi{dollar} or NK cells were incubated with dextran no significant IL-12 or {dollar}rm IFNgamma{dollar} production was observed. Both {dollar}rm mphi{dollar} and NK cells bound dextran to their surfaces. (Abstract shortened by UMI.)...