Human phagocytic cell response to histamine derived from potential probiotic strains of Lactobacillus reuteri.

Histamine derived from lactobacilli isolates is considered to be a potential immunomodulator able to interact with the host immune system. We tested the effect of pure histamine (0.413 mM) together with the effect of cell-culture supernatants (CCS) containing different concentration of histamine produced by two of Lactobacillus reuteri isolates on the activities of antioxidant enzyme, as well as on the phagocytic activity of human leucocytes (HL). Phagocytic activity represents the non-specific immune response of HL homogenate, in vitro. Analysed histamine-producers were represented by a goatling isolate named L. reuteri KO5 and a lamb isolate named L. reuteri E and histamine production was determined using HPLC method connected with UV detection. Concretely, the samples contained the mixture of isolated HL and the addition of lactobacilli CCS at three different final concentrations of histamine ∼ 0.1, 1.8 and 5.4 mM. It was found that pure histamine (0.413 mM) did not significantly influence the oxidant-antioxidant balance in HL demonstrated by unchanged degree of HL lipid peroxidation. However, at the same time, the final activity of catalase and superoxide dismutase were significantly changed (p ≤ 0.001). Moreover, the phagocytic index (p ≤ 0.01), lysozyme (p ≤ 0.05) and peroxidase activity (p ≤ 0.001), and production of IL-1β significantly decreased. CCS containing different concentration of produced histamine were also able to modulate the host non-specific immune response together with the enzymatic activity of SOD and catalase too. However, our findings indicated that the impact of lactobacilli histamine is strictly strain-dependent and concentration dependent. Moreover, it seems that histamine is not the only one lactobacilli metabolite, which may play an important role in overall immunomodulatory and antioxidant potential of tested lactobacilli.