Facing the enigma of immunomodulatory effects of intravenous immunoglobulin.

Intravenous immunoglobulin (IVIg) is a safe remedy for a number of conditions; it is produced from human plasma of thousands of healthy donors. The therapeutic effect of IVIg lies within its content. IVIg contains natural antibodies, which are more polyreactive than immune antibodies, including immunoglobulin G antibodies against endogenous and exogenous antibodies, immunomodulating peptides, and varies cytokines. Beneficial effects of IVIg have been established in immunodeficiencies, as well as in some autoimmune diseases. Also, numerous therapeutic effects of IVIg have been reported over the years in varies autoimmune diseases, recurrent pregnancy loss, and cancer. Many proposed immunoregulatory mechanisms of action of IVIg have been suggested. Some of them have been proven, others are still an enigma, at least in part. Some of these mechanisms entail (a) Fc-receptor blockade; (b) neutralization of pathogenic autoantibodies via idiotypic and anti-idiotypic antibodies; (c) effects on the Fas apoptotic pathway via agonistic and antagonistic anti-Fas autoantibodies; (d) regulation of complement components; (e) modulation of cytokine secretion; (f) hindrance of natural-killer cell activity; (g) inhibition of matrix metalloproteinase-9; (h) suppression of NFkB activation and IkB degradation; (i) G1 cell cycle arrest; (j) prevention of tumor growth; (k) decrease in leukocyte recruitment; (l) attenuation of T-cell stimulation; (m) effects on antibody kinetics; and (n) effects on dendritic cells. The variant mechanisms of IVIg are believed to cooperate in a synergistic way, which all together point to IVIg as a therapeutic preparation with anti-inflammatory, antiself-reactivity, antimetastatic, and embryo-protective effects. This article reviews several main mechanisms of IVIg in order to shed some light on the set of therapeutic effects of IVIg, which are not yet fully understood.