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Age influences recovery of systemic and mucosal immune responses following acute depletion of CD4 T cells.

We have examined the influence of recipient age on the recovery of the CD4 T cell compartment following in vivo treatment with anti-CD4. Mice were treated with anti-CD4 beginning in utero (adolescent), at 8 weeks (young adult), or at 52 weeks (old adult). Following acute CD4 depletion, adolescent mice recovered CD4 T cells rapidly (99% of age-matched controls at 5 weeks after anti-CD4 treatment). Young adult mice recovered more slowly (48% of control at 5 weeks), while old adult mice recovered less than 50% of control CD4 T cell numbers at 12 weeks after depletion. At 12 weeks after anti-CD4 treatment, adolescent mice made an enhanced anti-SRBC antibody response and young adult mice mounted a response comparable to their age-matched controls. In comparison, old adult mice mounted on anti-SRBC response that was only 57% that of their age-matched controls. By 1 week after cessation of anti-CD4 treatment, adolescent mice mounted normal systemic and intestinal responses to challenge with the thymic-dependent antigen cholera toxin (CT). In contrast, young adult mice recovered < 50% of age-matched control CT responsiveness by 5 weeks post-CD4 depletion. By 5 weeks post-CD4 depletion, young adult mice exhibited normal tolerance following enteric tolerization with ovalbumin. These findings underscore the importance of recipient age in designing or interpreting studies employing T cell depletion.