Acute stress may facilitate recovery from a subcutaneous bacterial challenge

The effects of stress on the immune system vary with both the duration and type of stressor. Many studies suggest that stress may compromise an organism's ability to recover from immune challenge. However, recent findings suggest that stress may actually enhance some aspects of immune function. For example, exposure to a single session (similar to 2 h) of intermittent inescapable tail-shocks (S) has been shown to activate the acute phase response and increase some aspects of macrophage function. Thus, the following experiments assessed whether IS exposure would alter local inflammation produced by peripheral injection of streptomycin-killed bacteria. Rats (Harlan Sprague Dawley) were exposed to IS (100 1.6-mA, 60 s variable intertrial interval) and injected with Escherichia coli (similar to 2.5 x 10(8) CFU s.c. posterior to the shoulder blades). The area of inflammation was measured until the inflammation had completely resolved (typically 7-8 days). When bacteria were administered immediately after S, rats resolved inflammation significantly faster than did nonstressed rats. Since adrenalectomy did not reduce the effect of S, it is unlikely that this effect is a result of elevated corticosterone levels. Furthermore, S does not appear to alter the rat's ability to sequester bacteria in the subcutaneous space since no swelling of lymph nodes or chronic activation of the hypothalamic-pituitary-adrenal axis was observed.