Association of human leukocyte antigen with outcomes of infectious diseases: the streptococcal experience.

The role of host genetic factors in determining susceptibility to infections has become more evident. Certain individuals appear to be predisposed to certain infections, whereas others are protected. By studying the immune response and the genetic makeup of susceptible and resistant individuals a better understanding of the disease process can be achieved. Infections caused by group A streptococci offer an excellent model to study host-pathogen interactions and how the host genetic variation can influence the infection outcome. These studies showed that the same clone of these bacteria can cause severe or non-severe invasive disease. This difference was largely related to the human leukocyte antigen class 11 type of the patient. Certain class II haplotypes present the streptococcal superantigens in a way that results in responses, whereas others present the same superantigens in a way that elicits very potent inflammatory responses that can lead to organ failure and shock. These findings underscore the role of host genetic factors in determining the outcome of serious infections and warrants further investigations into how the same or different genetic factors affect susceptibility to other emerging and re-emerging pathogens.