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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 data presented in this paper support a common source for intestinal mast cells in intestinal mucosae. IMC precursors and/or mastocytopoietic factors of as yet unknown origin could be transferred by immune mesenteric lymph node (IMLN) cells of thymus-bearing mice. The differentiated locally or induced mastocytopoiesis in Trichinella spiralis infected mucosal sites, but only in animals with a normal thymus function. Antigen-stimulated precursor cells either in the gut or in the mesenteric lymph node to enter the circulation and home to both parasitized and nonparasitized mucosal sites. Both proliferation in the mesenteric lymph node and in the intestinal mucosae were shown to be thymus-dependent. The injected IMLN stimulated only the proliferation of IMC and not of globule leucocytes. This might indicate that cells relevant for IMC proliferation are different from those essential for GL proliferation.

The recent identification of a T-cell-derived antigen-binding molecule (TABM), Trichinella spiralis factor (Tric-F), isolated from culture supernatants of lymphoid cells from mice infected with the intestinal helminth T. spiralis, has led to investigation of the ability of Tric-F to induce a T-cell-dependent feedback circuit that ultimately suppresses the production of other TABMs with similar (isotype-like) features. This form of regulation that has been identified in contact hypersensitivity and in delayed-type hypersensitivity (DTH) responses to tumor cells, was shown not to be antigen-specific but to be DTH-specific. Injection of mice with the TABM called picryl chloride factor (PCl-F) induced suppression of the production of DTH-initiating TABMs of other antigenic specificities. In this study, we report that intravenous injection of mice with Tric-F or PCl-F, 8 days before an oral infection with T. spiralis, induced suppressor cells that inhibited the T-cell-dependent influx into the gut of inflammatory cells, comprising mast cells and eosinophils. Similar results were obtained when the mice were skin sensitized with PCl 8 days prior to a T. spiralis infection, i.e. in a system where TABMs are known to be produced. The phenotype of these suppressor cells was Lyt-1-2+. This suppression preferentially affected the parasite-induced DTH-like response in the gut. In contrast, increased levels of IgA plasma cells in the gut, and worm expulsion were not affected by these treatments. In reciprocal experiments, intravenous injection of Tric-F, or PCl-F, or an oral infection with T. spiralis (that results in the production of TABMs) given 8 days before contact sensitizing mice with PCl, resulted in a suppression of elicitation of cutaneous DTH, as measured by ear swelling. In contrast, pretreatment with anti-dinitrophenyl IgE antibody did not interfere with intestinal inflammation to T. spiralis nor with DTH to PCl. Our results suggest that similar to cutaneous DTH, T. spiralis-specific T-cell factors are involved in the initiation and regulation of the DTH-like mast cell and eosinophil-rich intestinal inflammation that accompanies T. spiralis infections in the gut. Since both Tric-F and PCl-F induce suppression of cellular immune responses in vivo, independent of antigen specificity, it is concluded that Tric-F belongs to the same isotype of TABMs as PCl-F that therefore can be regulated by a non-antigen-specific, isotype-like, T-cell-dependent feedback mechanism.

The frequency of precursor cells capable of giving rise to cells with characteristics of mucosal mast cells in tissues from thymus-bearing and non-thymus-bearing (nude) mice orally infected with Trichinella spiralis was determined with an in vitro assay. Analysis of the frequency of mast cell precursors in bone marrow, blood, spleen and small intestinal tissue revealed similar frequencies of mast cell precursors in bone marrow from both thymus-bearing and athymic mice. These frequencies in bone marrow were not affected by infection. However, in blood and spleen from thymus-bearing mice at Day 7 post-infection (p.i.), and in the gut at Day 14 p.i., significant increases of mast cell precursor frequencies were detected. In contrast, no significant increase was observed in the tissues of infected nude mice. These data are in accordance with in vivo findings, indicating that a mucosal mast cell response in the gut is both thymus and antigen dependent. It was concluded that a mucosal mast cell response to infection with T. spiralis is probably due to local proliferation and maturation of residing mast cell precursors, that this response might be amplified by an influx of precursor cells from the blood into the gut, and that both phenomena are T-cell 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. The 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 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.

We have previously reported that intestinal mast cells represent a separate population of mast cells which is thymus- (T-) dependent. In this paper we examine whether the appearance of these cells is dependent on thymus-dependent antibodies or thymus serum factor(s). The response of intestinal mast cells and globule leucocytes to a Trichinella spiralis infection was therefore studied in congenitally athymic (nude) mice after treatment with specific anti-T. spiralis hyperimmune serum or normal mouse serum from thymus-bearing litter-mates. However, transfer of both types of serum did not lead to an intestinal mast cell response. It was concluded that the presence of an intact thymus or T-dependent cellular reactions and/or their products are essential for appearance of intestinal mast cells. In contrast infected athymic mice reacted with a minor reponse of globule leucocytes irrespective of the serum transfer. Occasionally metachromatic intra-epithelially located cells with toluidine-blue-positive granules, believed to be globule leucocytes, showed mitotic figures. Metachromatic cells were observed occasionally within the lumen of the gut. These data were interpreted as supporting the idea that the globule leucocyte is a cell sui generis and independent of the intestinal mast cell.

The involvement of serotonin in the regulation of intestinal mastocytopoiesis and inflammation has been investigated in mice infected with Trichinella spiralis. Two serotonin antagonists, methysergide and ketanserin, were examined for their ability to interfere with jejunal pathology comprising the influx of mucosal mast cells and other inflammatory cells during an infection with T. spiralis and with worm expulsion. In vitro analysis of the frequency of mast cell precursors in bone marrow, blood, spleen and intestinal tissue suggested that the mucosal mast cell response during a T. spiralis infection is probably due to invasion and local maturation in the gut of mast cell precursors, and may be mediated by T-cell-derived mast cell growth factors. Since both serotonin antagonists inhibited the mucosal mast cell response in T. spiralis-infected mice and diminished the influx of eosinophilic granulocytes, goblet cell hyperplasia, and villous atrophy, it was concluded that during a T. spiralis infection in mice release of serotonin may provide an environment that facilitates the local influx in the gut of inflammatory cells. Since worm expulsion was not affected by the serotonin antagonists, these results suggest that worm expulsion can occur without a mast cell and or eosinophilic granulocyte influx. The role of serotonin release by as yet unidentified serotonin-containing cells in the gut in relation with T cell regulation is discussed.

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.