T lymphocytes with receptors for IgM-Fc (Tμ) as an effector cell in delayed-type hypersensitivity

Abstract

BCG-immunized guinea pigs were challenged by PPD via footpad and changes in proportions of lymphocytes expressing receptors for Fc of IgM (Fcμ-R) and IgG (Fcγ-R) in draining lymph nodes were examined. Associated with development of DTH in footpad, the percentage of Fcμ-R + but not Fcγ-R + cells increased in the regional lymph nodes of guinea pigs immunized with BCG via footpad or through the subcutaneous route, either of which was highly immunogenic for the induction of DTH. Whereas, no percentage increase was seen with animals immunized through the intravenous route in which DTH was not induced by PPD. The percentage of Fcμ-R + cells started to increase as early as 3 or 6 hr after PPD injection prior to development of DTH, reaching a maximum at 12 hr, and returned almost to normal levels by 48 hr. The absolute numbers as well as percentages of Fcμ-R + cells markedly increased. Treatment of sensitized lymphocytes with anti-thymocyte serum and complement revealed that the increased Fcμ-R + cells were mainly included into a T-cell population (Tμ). Next, we prepared fractions enriched for or depleted of Tμ and those depleted of T cells with Fcγ-R (Tγ) from the lymph nodes of BCG-immunized inbred guinea pigs (strain 2) and injected them with 50 μg PPD intradermally into the unsensitized guinea pigs to examine their ability to transfer DTH. Both fractions enriched for Tμ and depleted of Tγ, but not those depleted of Tμ could transfer DTH. After treatment of Tμ fractions as well as unseparated T lymphocytes with anti-thymocyte serum almost completely abrogated their ability to transfer DTH. These results indicate that primed T cells responsible for DTH reaction may be included in the Tμ population.