Immunological memory in B‐cell‐deficient mice conveys long‐lasting protection against genital tract infection with Chlamydia trachomatis by rapid recruitment of T cells

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Abstract
The role of antibodies and antigen deposition for the development of immunological memory has been incompletely investigated. We addressed whether long-term protection and T-cell memory can be stimulated against a genital tract infection with human Chlamydia trachomatis serovar D in B-cell-deficient (µMT) mice. At 6 months following a primary infection with C. trachomatis, both µMT and wild-type (WT) mice exhibited strong and comparable protection against reinfection. Evidence of long-lasting CD4+ T-cell memory was found in both µMT and WT mice, typified by comparable delayed-type hypersensitivity (DTH) reactions against chlamydial antigens. No bacterial or chlamydial DNA was found in the genital tract of µMT memory mice, suggesting that immunological memory was maintained in the absence of antigen. Whereas few T cells were present in the genital tract of memory mice, rapid recruitment of CD4+, and some CD8+, T cells into the genital tract tissue was observed after challenge with live bacteria. Accumulation of T cells in the genital tract was preceded by a short transient infection of similar magnitude in both µMT and WT memory mice, arguing against a long-term protective role of local antibodies. The rapid recruitment of CD4+ T cells into the genital tract was associated with a transient detection of interferon-γ (IFN-γ) mRNA in the genital tract in chlamydia-immune memory mice, which was not found in naïve, challenged mice. Thus, long-term protection in the genital tract against C. trachomatis infection is conveyed by IFN-γ-producing CD4+ memory T cells, which appear to be maintained in the absence of antibodies and local antigen deposition.