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. 2014 Nov 21:805–892. doi: 10.1016/B978-0-12-397175-3.00019-3

FIGURE 19.15.

FIGURE 19.15

Region-specific immunity in the epididymis and vas deferens.

Activin A and its binding protein, follistatin, are inversely distributed in a distinctive proximal-to-distal pattern, with highest levels of activin A expression in the caput, and highest follistatin expression in the distal vas. Elevated production of activin A coincides with increased numbers and apparent activity of intra-epithelial immune cells, most notably dendritic cells, but also macrophages and CD8+ T cells. The immunoregulatory enzyme, indoleamine 2,3-dioxygenase (IDO), is highly expressed in the caput, with the exception of the region directly adjacent to the testis (initial segment). Susceptibility to sperm antibody formation following damage to the reproductive tract increases in a proximal-to-distal pattern, indicating a progressive decline in local immunoregulatory mechanisms.