Binding of monomeric immunoglobulins by bone marrow‐derived mononuclear phagocytes; its modulation by interferon‐γ

Abstract

The ability of resting and activated rat bone marrow-derived mononuclear phagocytes (BMMΦ) to bind monomeric rat, mouse, and human IgG was determined by means of flow cytometry. Rat IgG_2b bound with high affinity (K_d ≅ 3 × 10⁻⁹); binding was optimal at 4°C and was only little affected by trypsin treatment. The other IgG bound with only low affinity (rat IgG_2a, mouse and human IgG) or not at all to rat BMMΦ (rat IgG₁, rat IgG_2c). The binding of rat IgG_2b was not affected by the presence of a surplus of low-affinity binding IgG, and vice versa, indicating that high- and low-affinity IgG bind to different sites. Binding of high- and low-affinity IgG as well as expression of MHC class II molecules and of tumoricidal activity by BMMΦ was markedly enhanced by rat interferon-γ in low concentration (0.1 to 1.0 IU IFN-γ/ml). On the other hand, heat-killed Corynebacterium parvum organisms, that were equally potent in triggering tumoricidal activity, neither enhanced the binding of IgG nor the expression of MHC class II molecules by BMMΦ, suggesting that these abilities are not necessarily closely related phenomena.