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Intravenous immunoglobulin (IVIG) is a product prepared from fractionation of pools of thousands of plasma donations collected at blood transfusion services. IVIG has been used in the treatment of neurological disorders, primary and secondary immunodeficiency, skin disorders, autoimmune disorders, immunologic abortion, and as anti-cancer and anti-inflammatory therapy. In this paper we listed a number of diseases for which the use of IVIG has been successful and the most mentioned mechanisms of actions of this immunotherapy. IVIG has different modes of actions involving interference with activation of complement components and the cytokine network; effects on regulatory T cells (Tregs) subset; expression of Fc receptors; modulation of idiotype network; and activation, proliferation and effector functions of B and T lymphocytes and of antigen-presenting cells such as dendritic cells and macrophages. We concluded that IVIG has proven to be efficacious in the treatment of immunodeficiency, autoimmunity, infections and inflammatory disorders over the last three decades. To date IVIG has been used to treat more than 80 diseases. Although some of the mechanisms of actions of IVIG are obscure in nature, the fact that many patients improved with it when all other options of treatment were exhausted, make the use of IVIG an important alternative. On the other hand, treatment with IVIG is expensive. We are hopeful that in near future new horizons will be open for the acquisition and use of a cheaper IVIG to treat weak immune system or as immunosuppressive drug in the treatment of autoimmune and inflammatory disorders.

Streptococcal protein-G (SpG), type III bacterial Fc receptor, is a small globular protein produced by several Streptococcal species and it is composed of two or three nearly identical domains, each of 55 amino acids. Streptococcal protein G has been shown to have high binding affinity to sera from various mammalian species including rabbit, human, pig, goat, sheep, cow and many other animal species. Of concern are patients with invasive infections by Streptococcus spp, where large amount of secreted SpG could interfere with the outcome of the gel technique by getting false negative tests. It has been shown and reported that the bacterial protein SpA was already found to inhibit the Coomb's test. We hypothesize that SpG as well as many other immunoglobulin-binding bacterial proteins with binding affinity to human IgG could cause false negative results in patients with bacteraemia. With the intention of proving this hypothesis we conducted two sets of experiments, which proved that SpG has the potential of inhibiting the gel test for the detection of sensitized erythrocytes in vitro. We concluded that is important to exercise caution, when evaluating a result of gel technique in patients with septicemia caused by SpG-producer Streptococci. The experiments used in this research were novel modifications of existent techniques and they proved reliable in demonstrating our hypothesis.

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