Important components of the intestinal mucosal immunity are free intraepithelial and lamina propria lymphocytes involved in the regulation and activity of the immune response. The gut epithelium includes a heterogeneous T lymphocyte population, most of which are cytotoxic CD8 T cells, furthermore helper CD4 T cells, and regulatory T cells. In the lamina propria is present a large number of B cells and IgA-producing plasma cells, CD4 T cells, macrophages and dendritic cells.

This study detected the presence of helper CD4 and cytotoxic CD8 T lymphocytes, and B lymphocytes in the small intestine of mice treated with probiotic strains and infected with T. spiralis.

Bacterial strains of different origin (Enterococcus faecium AL41= CCM8558, Enterococcus durans ED26E/7, Lactobacillus fermentum AD1 = CCM7421, Lactobacillus plantarum 17L/1) were administered daily in dose of 10⁹CFU/ml in 100 µl and mice were infected with 400 larvae of T. spiralis on 7^th day of treatment.

L. fermentum AD1 and L. plantarum 17L/1 increased numbers of helper CD4 T cells in the epithelium and cytotoxic CD8 T cells in the lamina propria on 7^th day of administration (before parasitic infection). T. spiralis infection caused a significant inhibition of examined lymphocyte subpopulations from 5 to 25 days post infection (p.i.). Lactobacilli restored the CD4 T cell numbers in the epithelium and lamina propria on the level of healthy control from day 11 p.i. All strains stimulated the numbers of CD8 T cells in infected mice, but in comparison to control, CD8 T cells were reduced in the epithelium until day 25 p.i. and in the lamina propria only on day 5 p.i. An inhibition of B cells (CD19) in the small intestine after T. spiralis infection was not affected by probiotic therapy till day 25 p.i., but a stimulation of B cells was found after treatment with E. durans ED26E/7 and L. fermentum AD1 on day 32 p.i. The greatest anti-parasitic effect against adults was presented by E. faecium AL41 (65 % reduction). A significant decrease in the number of muscle larvae was detected in all treated groups (reduction 55 %). The obtained results confirmed the strain-specific immunomodulatory effect of probiotic bacteria. The greatest immunomodulatory potential on the gut CD4 and CD8 lymphocytes during T. spiralis infection was confirmed by L. fermentum AD1 and L. plantarum17L/1. It could be caused by a longer presence of Trichinella adults in the gut in contrast to mice treated with enterococci. The greatest protective effect against adults was presented by E. faecium AL41 and E. durans ED26E/7, strains producing enterocins that could influence mucin secretion. A significant decrease in the number of muscle larvae was detected in all treated groups. The CD8 T cell subpopulation was stimulated after probiotic treatment and it could prevent a migration of newborn larvae to the muscles.