Morphometric characteristics of effects induced by Ensifer meliloti lipopolysaccharide fractions on parenchymatous organs in laboratory rats with secondary immunodeficiency

Introduction. Gram-negative bacteria-derived lipopolysaccharides (LPS) are better known as bacterial endotoxins. However, an increasing body of evidence has been accumulated regarding a whole range of LPS-bound physiological effects also observed in normal settings. In particular, LPS derived from some bacterial species was shown to exhibit an immunomodulating activity.

Study objective — to characterize physiological effects of Ensifer meliloti lipopolysaccharides in modelled rat induced immunodeficiency.

Materials and methods. Biological activity of intraperitoneally administered E. meliloti LPS fractions was studied for 21 days in 60 outbred male rats after induction of a minimal immunodeficiency state 24 hours later after inoculating cytostatic agent cyclophosphamide (CF). Animals were euthanized on day 22 followed by conducting an autopsy and morphometric study of internal organs. Later, paraffin-embedded sections of parenchymal organs were stained with hematoxylin-eosin and examined histologically by light microscopy.

Results. It was found that at the end of the experiment cyclophosphamide applied to laboratory animals insignificantly decreased weight of liver and kidney, but not that of heart and spleen (compared to intact animals). In contrast, lung weight was solely significantly increased in immunodeficient rats compared to control. Intraperitoneally administered LPS fractions during secondary immunodeficiency affected weight parameters in the liver and kidney as the most intensively blood supplied organs suggesting its systemic effects. Quantity of follicles with large germinal centers as well as secondary follicles and lymphatic sheath formation in splenic stroma was increased that features activated immune response. Moreover, hepatic lymphoid infiltration in the portal tracts and reversal to normal vascular pattern were found as well. In contrast, LPS and Licopid administered to rats resulted in marked lung hyperplasia of lymphoid tissue containing large germinal centers.

Conclusion. The data obtained indicate that E. meliloti-derived LPS fractions administered to rats with secondary immunodeficiency positively affected immunoreactivity.