Fc fragments of human IgG may influence allergic reactions

A single dose of monoclonal anti-phencyclidine IgG offers long-term reductions in phencyclidine behavioral effects in rats

These studies tested the hypothesis that a single dose of high-affinity anti-phencyclidine monoclonal antibody (anti-PCP mAb) provides long-term protection against behavioral effects of repeated PCP administration in rats. Rats were treated with saline, nonspecific bovine IgG (NS-IgG), or anti-PCP mAb (1.0 g/kg). The next morning, the rats were challenged with escalating i.v. doses of PCP (0.32, 0.56, and 1.0 mg/kg) at 90-min intervals. This regimen was repeated every 3 days for 2 weeks. In the saline and NS-IgG control groups, PCP yielded reproducible and linear dose-dependent effects that remained constant during the experiment. In contrast, the anti-PCP mAb treatment blocked PCP effects on day 1, and sustained significant (P < 0.05) reductions in drug effects for the entire 2-week experiment. Brain PCP concentrations (determined at study termination) were reduced by ~55%, whereas serum concentrations were increased over 4000% compared with controls. Thus, a single dose of antibody medication provided long-term reductions in drug effects and brain concentrations, beyond the expected capacity of the drug-antibody interaction. These data challenge current concepts about in vivo dose dependence and unimolecular interaction between antibody binding sites and small molecules and establish that neuroprotection by mAbs may have an unique mechanism of action.

Aggregated immunoglobulin and Fc fragment of IgG induce IL-6 release from human monocytes

The Fc fragment of immunoglobulin (Ig) has been shown to play an important role in the regulation of humoral immunity, cellular immunity, lymphocyte and monocyte activation, and immune mediator secretion. We wished to determine if Ig or Fc fragments would induce IL-6 production from monocytes. Incubation of monocytes purified from human peripheral blood mononuclear cells with aggregated Ig or Fc fragments of Ig induced interleukin-6 (IL-6) activity in the supernatants. Monomeric Ig taken from an intravenous preparation of Ig, from which all aggregated Ig are removed, would not induce IL-6 production from monocytes whereas as a heat-treated aliquot, presumably containing aggregates, did induce IL-6. The supernatants were assayed according to their ability to induce growth in a murine hybridoma cell line B9, or enhance Ig secretion of B cells stimulated with Staphylococcus aureus Cowan 1 (SAC). The IL-6 activity in the supernatants could be neutralized by a polyclonal rabbit anti-human IL-6 antiserum in both assays of IL-6 activity. Exposure of T-enriched or B-enriched lymphocyte subpopulations to Fc fragments did not induce the release of any IL-6 after 12 hr of incubation, but small amounts of IL-6 were produced by B-enriched cells after 60 hr of exposure to Fc fragments. Hence Fc fragments and aggregated Ig induce peripheral blood monocytes to rapidly secrete large quantities of interleukin-6.

Fc fragment from human IgG induces PGE2 secretion. II. Negative regulation in B cell differentiation

In humans, in vitro, Fc fragment of IgG at a low concentration induces plasma cell generation. However, Fc fragment at a high concentration induces PGE2 release of monocyte activation capable of inhibiting this differentiation. The levels of PGE2 in the supernatant culture from mononuclear cells from normal donors were examined as a function of culture duration and concentration of Fc, Fab fragments and IgG. Plasma cells containing intracytoplasmic Ig were demonstrated by immunofluorescence with a polyvalent antiserum to human immunoglobulin(s). PGE2 levels, from mononuclear cell cultures, were analyzed by the RIA test. The results indicated that the Fc fragments are able to induce PGE2 secretion. The maximal release of PGE2 occurs after 24 hr of culture; this level is proportionate to the quantity of Fc fragments introduced. The addition of indomethacin in the cell culture stimulated by a high concentration of Fc fragments reestablishes the percentage of plasma cells. These results suggest the regulatory role of Fc fragment by PGE2 secretion in B cell differentiation.