The C3H UV-induced fibrosarcoma, 1591, is highly immunogenic and, therefore, is readily rejected when transplanted into immunocompetent syngeneic recipients. Previous analysis of 1591 with tumour-specific or H-2-reactive monoclonal antibodies revealed that this antigenicity might be due to the expression of two novel class I major histocompatibility complex (MHC) antigens. In this report we describe the molecular cloning and initial characterization of three genes which account for all of the unique serological class I reactivities observed on this tumour. These include two distinct, but highly conserved, H-2L-like genes, and a third gene the product of which bears determinants which are characteristic of both the tumour and of class I products of the H-2k haplotype. Moreover, each of these genes contains a polymorphic restriction enzyme fragment which is detected in the class I sequences of 1591 relative to normal C3H tissue. Since the expression of these polymorphic class I sequences is relevant to the immunogenicity of 1591, the mutational events by which these genes were generated may be significant to the immunobiology of this tumour.

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PubMedDate not supplied

Immunolocalization of NBC3 and NHE3 in the rat epididymis: colocalization of NBC3 and the vacuolar H+-ATPase.

In the male reproductive tract, the epididymis plays an important role in mediating transepithelial bicarbonate transport and luminal acidification. In the proximal vas deferens, a significant component of luminal acidification is Na+-independent, and mediated by specific cells that possess apical vacuolar proton pumps. In contrast, luminal acidification in the cauda epididymidis is an Na+-dependent process. The specific apical Na+-dependent H+/base transport process(es) responsible for luminal acidification have not been identified. A potential clue as to the identity of these apical Na+-dependent H+/base transporter(s) is provided by similarities between the transport properties of the epididymis and the mammalian nephron. Specifically, the H+/base transport properties of caput epididymidis resemble the mammalian renal proximal tubule, whereas the distal epididymis and vas deferens have characteristics in common with renal collecting duct intercalated cells. Given the known expression of the Na+/H+ antiporter, NHE3, in the proximal tubule, and of the electroneutral sodium bicarbonate cotransporter, NBC3, in renal intercalated cells, we determined the localization of NHE3 and NBC3 in various regions of rat epididymis. NBC3 was highly expressed on the apical membrane of apical (narrow) cells in caput epididymidis, and light (clear) cells in corpus and cauda epididymidis. The number of cells expressing apical NBC3 was highest in cauda epididymidis. The localization of NBC3 in the epididymis was identical to the vacuolar H+-ATPase. The results indicate that colocalization of NBC3 and the vacuolar H+-ATPase is not restricted to kidney intercalated cells. Moreover, the close association of the two transporters appears to be a more generalized phenomenon in cells that express high levels of vacuolar H+-ATPase. Unlike NBC3, NHE3 was most highly expressed on the apical membrane of all epithelial cells in caput epididymidis, with less expression in the corpus, and no expression in the cauda. These results suggest that apical NBC3 and NHE3 potentially play an important role in mediating luminal H+/base transport in epididymis.

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