The diversity and heterogeneity of biologic reactions is a condition sine qua non for the adaptation of live organisms to changes of external environment. Reactions of the immune system enable survival even in extreme conditions. Modern medicine often reaches situations never met by the organism in phylogenesis. Thanks to up-to-date therapeutical approaches many patients survive with grave symptoms such as multiple organ failure and extensive forms of injury. New infectious diseases are emerging, e.g. HIV/AIDS. Notwithstanding the broad array of external insults, it becomes obvious that organisms mobilize defence reactions according to a general scheme. Likewise, exhaustion of the immune potential occurs according to an archetypal pattern. In the case of cell-mediated immunity the faultless course of which is of critical importance for organisms in extreme conditions, the loss begins with the absence of reactivity of T-cells to specific antigens to end with the absence of their reactivity to polyclonal mitogens. The article deals with pathogenic mechanisms underlying the onset of immunodeficiencies caused by both infectious and non-infectious stimuli with special regard being focused on cardiac surgery in extracorporeal circuit.