Microbial Immunosuppression

Immunosuppression is a condition characterized by immune dysfunction at either cellular or humoral levels [1]. Defective cellular levels include alterations in neutrophils, monocyte/macrophage, and natural killer (NK) cells for innate immunity or alterations in B or T lymphocytes for adaptive immunity [2, 3]. In contrast, immune dysfunction at the humoral level is largely due to alteration in soluble factors mediated by complement or chemokines for innate immunity [4] or due to alteration in antibodies or cytokines for adaptive immunity [5]. Most of these alterations are congenital in nature as evidenced in patients with primary immunodeficiency diseases. The defective compartment of the immune system determines the proclivity of the invading pathogens and the contracted infection is usually disseminating. Consequently, the inflicted immunosuppression is permanent unless reconstituted by immunoglobulin transfusions or bone marrow transplantation. On the other hand, secondary immunosuppression may be internal as a consequence of excessive adenosine release [6] into the extracellular space as evidenced in multiple organ failure (e.g. pancreas, kidney, liver) or it might be externally induced by a number of causal agents including infectious pathogens, immunosuppressive drugs, antimicrobial drugs, and anti-neoplastic drugs. The causal, pathophysiology, and methods used to evaluate immunosuppression due to pathogens are the focus of this chapter.