Immunohistochemical detection of macrophage migration inhibitory factor in fetal and adult bovine epididymis: Release by the apocrine secretion mode?

Originally defined as a lymphokine inhibiting the random migration
of macrophages, the macrophage migration inhibitory factor (MIF) is
an important mediator of the host response to infection. Beyond its
function as a classical cytokine, MIF is currently portrayed as a
multifunctional protein with growth-regulating properties present
in organ systems beyond immune cells. In previous studies, we
detected substantial amounts of MIF in the rat epididymis and
epididymal spermatozoa, where it appears to play a role during
post-testicular sperm maturation and the acquisition of
fertilization ability. To explore its presence in other species not
yet examined in this respect, we extended the range of studies to
the bull. Using a polyclonal antibody raised against MIF purified
from bovine eye lenses, we detected MIF in the epithelium of the
adult bovine epididymis with the basal cells representing a
prominently stained cell type. A distinct accumulation of MIF at
the apical cell pole of the epithelial cells and in membranous
vesicles localized in the lumen of the epididynnal duct was
obvious. In the fetal bovine epididymis, we also detected MIF in
the epithelium, whereas MIF accumulation was evident at the apical
cell surface and in apical protrusions. By immuno-electron
microscopy of the adult bovine epididymis, we localized MIF in
apical protrusions of the epithelial cells and in luminal
membrane-bound vesicles that were found in close proximity to sperm
cells. Although the precise origin of the MIF-containing vesicles
remains to be delineated, our morphological observations support
the hypothesis that they become detached from the apical surface of
the epididymal epithelial cells. Additionally, an association of
MIF with the outer dense fibers of luminal spermatozoa was
demonstrated. Data obtained in this study suggest MIF release by an
apocrine secretion mode in the bovine epididymis. Furthermore, MIF
localized in the basal cells of the epithelium and in the
connective tissue could be responsible for regulating the migration
of macrophages in order to avoid contact of immune cells with
spermatozoa that carry a wide range of potent antigens. Copyright
(c) 2006 S. Karger AG, Basel.