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infectious immunity

Monday 16 March 2009

Injurious Effects of Host Immunity

The host immune response to microbes can sometimes be the cause of tissue injury. This is best exemplified by the immune response to mycobacteria.

The granulomatous inflammatory reaction to Mycobacterium tuberculosis is a delayed hypersensitivity response that sequesters the bacilli and prevents spread, but also can produce tissue damage and fibrosis.

Similarly, the liver damage following hepatitis B virus infection of hepatocytes is mainly due to the immune response to the infected liver cells and not to cytopathic effects of the virus.

The humoral immune response to microbes also can have pathologic consequences.

For example, following infection with β-hemolytic streptococci, antibodies produced to the streptococcal M protein can cross-react with cardiac proteins and become deposited in the heart, and lead to rheumatic fever.

Poststreptococcal glomerulonephritis, which also can develop following infection with β-hemolytic streptococci, is caused by antistreptococcal antibodies that form complexes with streptococcal antigens and deposit in renal glomeruli and produce nephritis.

Thus, antimicrobial immune responses can have beneficial and pathologic consequences.