Effects of human calprotectin (L1) on in vitro immunoglobulin synthesis

Calprotectin (L1) is a major cytoplasmic protein of neutrophilic granulocytes and monocytes/macrophages which is released from leucocytes during activation or cell death. Apart from in vitro antimicrobial and antiproliferative activity little is known about the biological function of the protein. Since previous investigations have shown that calprotectin plasma levels are elevated in various inflammatory rheumatic diseases, we wanted to investigate if calprotectin has an effect on immune cell functions. Peripheral blood mononuclear cells, either unstimulated or polyclonally stimulated with mitogen, were incubated with calprotectin and effects were assessed by enumeration of immunoglobulin secreting cells (ELISPOT). The results indicate that incubation with high concentrations of calprotectin (> 64 micrograms/ml) inhibit the production of the three classes of immunoglobulins investigated (IgG, IgM and IgA), both for mitogen stimulated and unstimulated lymphocytes. Except for the highest concentration of calprotectin (500 micrograms/ml), it seems plausible that the observed inhibitory effect of calprotectin on Ig production is not a result of a direct toxic effect of calprotection on B lymphocytes. Altogether, these effects of high calprotectin levels might be of importance in the immunoregulation of inflammatory conditions.