Thymosin restoration of cellular immunity to Blastomyces dermatitidis in T-cell-depleted mice.

The immunopotentiating properties of thymosin in thymectomized, lethally irradiated, bone marrow-reconstituted mice (ThyXBM) were characterized, using footpad sensitivity to Blastomyces dermatitidis. Normal mice were shown to exhibit increasing delayed-type hypersensitivity responses to killed yeast cells of B. dermatitidis after injections of the organism on days 0 and 7, as measured by footpad swelling tests. The footpad response of normal thymosin-treated mice was similar to that of normal, non-thymosin-treated mice. ThyXBM mice were unable to elicit a footpad response when similarly injected and footpad tested with B. dermatitidis. Thymosin-treated ThyXBM mice responded to footpad testing at a level that was 62% greater than the response seen in non-thymosin-treated ThyXBM mice. This peak response occurred on day 12. The results indicated that thymosin was unable to enhance immune responses of normal intact mice but could restore immunocompetence in a T-cell-depleted host, as measured by footpad sensitivity to B. dermatitidis.