Review: immunomodulatory activity of pregnancy-associated plasma protein-A.

This mini-review highlights the growing number of indications for the immunological importance of pregnancy-associated plasma protein-A (PAPP-A), which is a remote member of the alpha-macroglobulin plasma protein family. PAPP-A can bind a variety of cytokines and specifically cleave a binding protein for insulin-like growth factors, thereby serving as a modulator of cytokine activity. Important immune functions, such as lymphocyte proliferation response to alloantigens and lectins and expression of HLA-DR molecules are predominantly suppressed in vitro by PAPP-A. It is likely that the immunoregulatory properties of PAPP-A are very similar to that of alpha 2-macroglobulin. The experimental data allows us to suppose that PAPP-A serves to prevent the recognition of the fetus by the maternal immune system and to suppress locally the host's immune response to the tumour.