In this study, we used a murine model of food-induced enteropathy in order to compare the morphological and immunostimulatory effects of the orally administered bovicin HC5. In our positive control group, the breakdown of mucosal tolerance was obtained by oral administration of the non-tolerogenic antigen ovalbumin (OVA). OVA has become a reference protein for immunological and biochemical studies, being widely used as an antigen for studying allergic diseases in mice .
The model used to induce food enteropathy worked properly, and an inflammatory reaction was developed in the small intestine. OVA administration altered the small intestinal architecture, increased protein permeability, caused edema and decrease the mucosal thickness in the large intestine. In contrast, upon oral administration of bovicin HC5, only minor histological alterations indicative of inflammation or alterations on permeability were observed, although an atrophy of the villi and destruction of the apical portion of the villi were detected in some regions of the small intestine.
The degree of impairment of the small intestine could explain the differences observed in weight gain between Bov and PC groups throughout the experiment, since these alterations may have influenced the absorption of nutrients. Saldanha et al. reported that BALB/c mice previously sensitized lost weight after challenging with OVA, which remained until the end of the experiment.
In normal conditions, the number of mast cells in the intestine is relatively constant, but hyperplasia can be observed during inflammatory reactions or during stages of remodeling/repair of inflammatory disorders . As a result of the food enteropathy developed upon administration of OVA, we observed increased number of mast cells in the small intestine of PC group. However, no alterations were observed in the mast cell population from the Bov group.
Bacterial products or cell components may induce metaplasia, proliferation and hypersecretion of goblet cells . In this study, animals treated with OVA showed reduced number of goblet cells in the small intestine, and a reduction in the secretion of acidic and neutral mucins. In contrast, the administration of bovicin HC5 did not alter the total number or the pattern of goblet cell secretion. The mucus protects the intestinal wall by limiting the absorption of antigens, and therefore, the hypersecretion of mucopolysaccharides was expected at the PC group, as a characteristic of allergic inflammation and as a result of increased IL-13 expression ; therefore, the reduction in the number of cells responsible for mucus secretion observed in PC group may not be related to the reduction in the secretion process per se, but to the limited count fields resulting from the destruction of the villi observed in PC group.
Similar to goblet cells, Paneth cells also play an important role in host intestinal defense mechanisms, contributing to the maintenance of the gastrointestinal barrier by secreting antimicrobial peptides and other compounds in response to bacteria and bacterial antigens [22, 23]. The presence of antigens in the gastrointestinal tract also influence the expression and activity of key proteins involved in the regulation of cell proliferation . Hypertrophy of Paneth cells and increased mitotic activity were observed in Bov and PC groups, indicating that despite the loss of villi architecture, secretion of antimicrobial compounds and tissue repair systems remained active, probably as a response to the injuries caused by bovicin HC5 and OVA in the small intestine.
Our results indicate that the effects of bovicin HC5 and ovalbumin administration are more pronounced in the intestine, which can explain the significant reduction in spleen cellularity observed in Bov and PC groups: immune cells probably migrated from the spleen to the intestine, where the main effects were observed.
OVA administration modulated the gut mucosal immunity in BALB/c mice towards significant TH2-polarized response, increasing the relative expression of IL-4, IL-5 and IL-13 mRNA. Goya et al. also observed increased mRNA levels of the TH2 cytokines IL-4, IL-5 and IL-13, as well as a decrease of INF-γ expression in the lungs of OVA-treated mice. A down modulation of regulatory mechanisms, with reduction of TGF-β and IL-10 expression, may be involved in the development of food allergy , but this pattern of cytokine expression, although expected, was not observed in this study.
The modulation of the host immune system induced by bacteriocins is a phenomenon much less understood when compared to other peptides or proteins, such as proteins extracted from mushrooms (such as LZ-8 (13 kDa) , Fip-vvo (15 kDa)  and FIP-fve (114 aa) ) and host-defense peptides [30, 31].
In contrast to the TH2-polarized response elicited by OVA, higher mRNA expression for the TH1 cytokines TNF-α, IL-12 and INF-γ were observed in the intestine of bovicin HC5-fed mice. Liu et al.  also demonstrated significant induction of IFN-γ after administration of the yam tuber storage protein dioscorin. Human cathelicidin LL-37 modulated the activity of IFN-γ on a variety of cell types , and pre-treatment with LL-37 induced IFN-γ production by monocytes, enhancing monocyte-derived dendritic cell functions, such as IL-12 secretion and TH1-polarized co-stimulatory activity .