Interleukin‐12 profoundly up‐regulates the synthesis of antigen‐specific complement‐fixing IgG2a, IgG2b and IgG3 antibody subclasses in vivo

Abstract

The influence of the cytokine interleukin-12 (IL-12) on humoral immune responses was studied in vivo. CBA/J mice immunized with protein antigens (keyhole limpet hemocyanin, phospholipase A2) adsorbed to aluminum hydroxide (Alum) develop a Th2-like immune response characterized by the production of large amounts of IgG1 as well as some IgE but little IgG2a, IgG2b and IgG3 antibodies. IL-12 is a cytokine that promotes the development and the activation of Th1 cells. Th1 cells are involved in the induction of cellular immunity, which is characterized by low or absent antibody production. On the other hand, some Th1-like immune responses are associated with a strong antibody production of the IgG2a, IgG2b and IgG3 subclasses. Thus, we investigated whether treatment with IL-12 would down-regulate the humoral immune response or stimulate antibody production of the IgG2a, IgG2b and IgG3 subclasses. We observed that: 1) administration of IL-12 to mice together with protein antigens adsorbed to Alum strongly enhanced the humoral immune response by increasing the synthesis of antigen-specific antibodies of the IgG2a, IgG2b and IgG3 subclasses 10- to 1000-fold. The synthesis of IgG1 was not or only slightly (2-5-fold) enhanced, whereas that of the IgE isotype was suppressed. 2) These effects of IL-12 were observed when high (10 micrograms, 100 micrograms) or low doses (0.1 microgram) of antigen were used for immunization. 3) Titration of IL-12 in vitro revealed that IgG2a is strongly up-regulated over a wide dose range of IL-12 (10 to 1000 ng/day). 4) The effects of IL-12 in vivo are at least partially interferon (IFN)-gamma-dependent because an anti-IFN-gamma mAb in combination with IL-12 prevented most of the enhanced IgG2a production. 5) Mice receiving IL-12 showed a strong up-regulation of IFN-gamma but no inhibition of IL-5 synthesis by spleen cells activated ex vivo with antigen. These results suggest that IL-12 is a potent adjuvant for enhancing humoral immunity to protein antigens adsorbed to Alum, primarily by inducing the synthesis of the complement-fixing IgG subclasses 2a, 2b and 3.

Complement Is Essential for Protection by an IgM and an IgG3 Monoclonal Antibody Against Experimental, Hematogenously Disseminated Candidiasis

“…These animals showed not only essentially identical patterns of increased susceptibility to mAb B6.1 when FNMS was used to replenish complement activity, but mAb C3.1 behaved in a similar fashion. mAb C3.1 is also a protective Ab with apparently identical epitope specificity as mAb B6.1, but mAb C3.1 is an IgG3 (23) and also should be a strong activator of complement (54). The acute lethality response was not due to metabolically active fungi, because formalin-killed yeast cells also caused the response.…”

Suppression of Immune Response and Protective Immunity to a Japanese Encephalitis Virus DNA Vaccine by Coadministration of an IL-12-Expressing Plasmid

“…Previous studies have shown that IL-12 can either enhance or inhibit humoral immunity, depending on the immunoglobulin isotype. Administration of recombinant IL-12 with protein Ag resulted in a significant increase of Th1-associated IgG2a, IgG2b, and IgG3 Ab response (36,37), whereas the Th2-associated IgG1 response was usually suppressed (38). In most studies of DNA vaccines, codelivery of the IL-12 gene was found to selectively increase IgG2a Ab, but had little effect or even decreased the total Ab titers (8, 39 -41).…”

Intranasal Administration of Recombinant Mouse Interleukin‐12 Increases Inflammation and Demyelination in Chronic Experimental Autoimmune Neuritis in Lewis Rats

“…Humoral immunity is also affected by IL-12. rmIL-12 decreases immunoglobulin G 1 (IgG 1 ) production and enhances the production of IgG 2a [16]. A major function of IL-12 seems to be in the defence against infectious diseases, especially those caused by intracellular microbes, this defence mechanism critically involves Th1 lymphocytes.…”