Distribution of human colonic dendritic cells and macrophages.

To define the phenotype of intestinal dendritic cells and macrophages, resected colonic specimens were used to obtain lamina propria cell suspensions by EDTA treatment, then enzymatic digestion. The phenotype of dendritic cell-enriched suspensions was compared with that of macrophage-enriched populations by immunocytochemistry using the avidin-biotin-peroxidase (ABC) system and immunoelectron microscopy. Dendritic cells expressed HLA-DR (L243) and HLA-DQ-associated (RFD) antigens and CD68 in a perinuclear distribution. Staining for S100 was weak or absent. Macrophages also expressed HLA markers (L243 and RFD1) and CD68. The 25F9 antigen was expressed strongly, whilst CD14 was absent from cells isolated from noninflamed tissues. To determine their anatomic distribution, immunohistochemistry was performed using single- and double-labelling techniques (ABC +or- alkaline phosphatase anti-alkaline phosphatase method). Mutually exclusive subsets of 25F9+ and S100+ cells were seen: 25F9+ macrophages were concentrated in a band immediately beneath the luminal epithelium; S100+/HLA-DR+ dendritic cells formed a reticular network throughout the lamina propria and beneath the basement membrane of the crypts. This distribution suggests that macrophages may help regulate intestinal responses by acting as the first line of defence against the entry of luminal antigens. A breach of the macrophage 'barrier' by invading antigens may necessitate the recruitment of T cell responses by immunostimulatory dendritic cells.

Fumonisin B1 production and vegetative compatibility of strains from Gibberella fujikuroi mating population 'A' (Fusarium moniliforme).

We examined 25 strains of Fusarium moniliforme from eight states known to be associated with equine leukoencephalomalacia, a disease caused by the mycotoxin fumonisin B1. We determined the mating population, mating type, and vegetative compatibility group to which each of these strains belonged. All 25 strains were in the 'A' mating population; 12 were A+ and 13 were A-. Seventeen of the 25 strains were female fertile; these strains also averaged higher levels of fumonisin B1 production than did the strains that were female sterile. Nitrate non-utilizing (nit) mutants were generated in all 25 strains and each strain was assigned to a unique vegetative compatibility group based on the inability of the derived nit mutants to form a prototrophic heterokaryon with complementary nit mutants derived from any of the other strains examined. From these data, we concluded that the production of fumonisin B1 is a general characteristic of strains from the 'A' mating population of Gibberella fujikuroi associated with equine leukoencephalomalacia, since all 25 of the isolates that we examined were genetically distinct individuals.

Two Different h Mating Types in SCHIZOSACCHAROMYCES POMBE.

In the strains of Schizosaccharomyces pombe introduced by Leupold (1950, 1958) into genetic research, heterothallic and homothallic mating types are known. The mating types are determined by two closely linked genes. We show that two distinct heterothallic - mating types exist: a stable one (h(-S)) and an unstable one (h(-U)), which can mutate to heterothallism + and homothallism. A proposal for incorporation of the new mating type h(-U) into Leupold's two-gene scheme is discussed.