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The effect of treatment with anti-thymocyte serum (ATS) or neonatal thymectomy with or without thymus reconstitution on the presence and proliferation of intestinal mast cells (IMC) and globule leucocytes (GL) was studied in the small intestine of the rat during and oral Trichinella spiralis infection. ATS exerted an initial transient inhibitory effect on the IMC response and a marked inhibitory effect on the GL response to an oral Trichinella infection. Neonatal thymectomy decreased numbers of IMC but not of GL in the non-infected rat. Thymus reconstitution restored IMC numbers, however, not to normal values. The IMC response to Trichinella was comparable in thymectomized, thymectomized and reconstituted and intact animals. In contrast, the degree of GL response to Trichinella depended mainly on the presence of a thymus. The combined results were interpreted in favour of the hypothesis that the origin of IMC is thymus (T)-dependent, and the response to Trichinella thymus independent. No evidence for the hypothesis that subepithelial IMC are precursors for the intra-epithelially located GL was found. The latter were regarded as an independent cell population, its origin being thymus independent, and its reaction to Trichinella mainly thymus dependent.

Mast cells have been studied in the mucosa and connective tissue of 28 biopsies of human duodenum. They were collected from individuals who for various reasons had to undergo upper intestinal endoscopy. Tissues were fixed in both standard formalin and a formalin-acetic acid (FA) fixative developed for visualization of mucosal mast cells. With both fixatives connective tissue mast cells (CTMC) were equally well recognized. Only with the FA fixative, an additional population of mast cells was observed both in the mucosa and the connective tissue. This population consisted of round cells, always smaller than CTMC, with a number of granules staining violet with toluidine blue. These mast cells comprised two cell types, differing in size, the larger being present in both the mucosa and the connective tissue, the smaller ones in a subepithelial position in the crypts of Lieberkühn and in the adjacent submucosa. It was suggested that this first mentioned additional population was similar to the mucosal mast cells (MMC) observed in rats and mice. The subepithelially located metachromatic cells differed in morphology from the globule leukocytes found in rats and mice. It was concluded that in the human duodenum a population of cells with MMC staining characteristics is present, which can only be visualized under special fixation conditions. Their further characterization and role in various disease conditions remains to be elucidated.

The anti-parasite response was investigated after oral infection of athymic nude (rnu/rnu) rats and heterozygous (+/rnu) littermates with 1000 muscle larvae of Trichinella spiralis. No IgM, IgG and IgE antibodies were detected in serum of rnu/rnu rats. Expulsion of adult worms from the small intestine was prolonged (worms were nearly all expelled at days 14 and 91 in +/rnu and rnu/rnu rats respectively). The yield of muscle larvae in the carcasses of nude rats at day 91 was 33 times higher than in +/rnu rats. In contrast to the strong inflammatory reaction in the parasitized tongue of +/rnu rats, no infiltration was observed in rnu/rnu rats. Using an immunoperoxide method with monoclonal anti-rat T-cell antibody, no T cells were identified in spleen, mesenteric lymph node and Peyer's patches. These data support earlier studies that the nude rat lacks functional T cells. As the counts of connective tissue mast cells (CTMC), intestinal mast cells (IMC) and globule leucocytes (GL) in small intestine of uninfected rnu/rnu rats were equal or higher than in +/rnu rats, it is concluded that the origin of these cells is thymus-independent. In contrast to +/rnu rats, infection of rnu/rnu rats induced no increase of CTMC, IMC or GL. Thus, these cells depend on T cells to undergo proliferation. Finally, results of this study were inconclusive whether IMC are precursors for GL, or that they represent independent cell populations.

The mast cell response in the mucosa and connective tissue of 36 jejunal biopsies of patients with clinically diagnosed trichinellosis, teniasis and lambliasis has been studied. Biopsy material was fixed in standard formalin or Carnoy’s fixative, enabling differentiation between mucosal mast cells (MMC) and connective tissue mast cells (CTMC). With both fixatives CTMC could equally well be recognized. With Carnoy’s fixative an additional population of mast cells (MMC) could be visualized both in the mucosa and the connective tissue. In the mucosa small mucosal mast cells were observed as well. Compared to the numbers of mast cells in the mucosa and the connective tissue of teniasis and lambliasis patients, the number of mast cells in trichinellosis patients only visualized using Carnoy’s fixative was markedly higher. It was concluded that also in man trichinellosis is accompanied by an increase of cells with MMC characteristics. Further studies are needed to clarify the morphological and histochemical features of these cells and their possible role in this parasitic infection.

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The relationship between the gut and mesenteric lymph node in the kinetics of mucosal mast cells (MMC) was further analysed. A Trichinella-induced synchronous proliferation of MMC occurred in the intestine of thymus-bearing and not in athymic mice, both at sites of parasite invasion (jejunum) and elsewhere (caecum) and in the mesenteric lymph node. The mastocytopoietic ability could be adoptively transferred with immune mesenteric lymph node cells to the jejunum and caecum of infected thymus-bearing recipients. The enhanced mastocytopoiesis which was both antigen- and thymus-dependent, was only observed for the stroma intestinal mast cells (IMC) and not for the intraepithelially located globule leucocytes (GL). The data suggest a common source for IMC in intestinal mucosae and support the idea that IMC and GL are two independent cell populations.

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