[Immune status of rats fed standard diets differing in antigen profile]

The enrichment of the food industry's resource base through novel food and raw materials necessitates the improvement of protocols for allergological safety assessment of such products. An important applied task in ensuring reliable results in allergy studies in vivo is the formation of basic diets. The nutrient composition of the diet and its antigen profile can directly or indirectly modulate the immune response of experimental animals, both through direct interaction with immune cells, including dendritic cells and T-lymphocytes, and through the secretion of chemokines and cytokines, thereby leading to distortion or misinterpretation of the data obtained. The widening of the list of sensitive indicators characterizing the protective potential of animals in the context of novel food allergenicity assessment has determined the need to standardize the antigenic profile of diets and minimize their modulating effect on the immune system. The purpose of the study was to investigate the effect of standard diets differing in ingredients and antigen profile on the immune status of rats.

A 30-day experiment was conducted on male Wistar rats with an initial body weight of 179±2 g. The animals were 45 days old at the beginning of the study. The rats were divided into two groups: Group 1 received a natural grain diet (the «NGD group») throughout the study period, while Group 2 received a semi-synthetic casein diet (the «SSD group»). A comprehensive assessment of the diets with different composition and antigen profile was performed using an extended pool of indicators of the immune status of rats: serum cytokine profile (G-CSF, GM-CSF, GRO/KC, IFN-γ, IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-10, IL-12p70, IL-13, IL-17A, IL-18, M-CSF, MCP-1, MIP-1α, MIP-3α, RANTES, TNF-α, VEGF), serum level of immunoglobulins (IgG1 and IgG4), pathomorphological and morphometric characteristics of immunocompetent organs (thymus, spleen, Peyer's patches of the small intestine).

A natural grain diet activates proinflammatory and Th2 pathways: significantly increased levels of IL-1β, IL-4, IL-7, and GM-CSF were detected in rats from the NGD group - by 43, 34, 42 and 16%, respectively (p<0.05) compared to those in the SSD group. Elevated level of IL-1β and IL-4 (the key cytokines involved in the type 2 immune response) declare an allergic immune reaction. Morphometric studies of the thymus in animals of the NGD group demonstrated an increase in the trabeculae width by 53% (p<0.05), compared with the SSD group, which indicates a response of the thymus to antigenic stimulation of a sensitized organism.

The results of assessing the immune status of rats fed standard diets differing in compositions and antigen profiles revealed a number of biologically significant systematic changes in the studied parameters. A natural grain diet, in contrast to a semi-synthetic ca sein diet, is characterized by the presence of ingredients with more pronounced sensitizing properties, therefore, it increases the level of immune stress in animals due to excessive production of pro-inflammatory cytokines and regulators of the humoral immune response. Within the standardization framework of basic diets for laboratory rodents used to assess the allergenic potential of food, including novel food, a semi-synthetic casein diet that does not cause increased antigenic stimulation of the immune system and meets the animals' physiological requirements may be recommended.