Immunobiochemical indices in clinically healthy horses and horses with equine infectious anemia

Aim. Equine infectious anemia (EIA) remains an urgent problem for many countries. This article presents the initial comprehensive comparative analysis of the immunobiochemical profiles of clinically healthy horses and those afflicted with the EIA in the western region of Ukraine. To address this objective, the immunobiochemical indices in healthy horses in the western region of Ukraine, the seasonal and age-related dynamics of the content of circulating immune complexes (CIC), vitamin C, and lysozyme were investigated. A possible association between the increase in the CIC rate and the content of serum fractions of protein and immunocompetent cells in horses with asymptomatic EIA course was determined. Methods. The study encompassed 329 non-purebred male and female horses of various age groups, comprising 225 EIA-free horses and 104 horses with asymptomatic EIA. Common serological and bio- chemical methods were employed, and identification of horses with EIA was accomplished via agar gel immunodiffu- sion assay with diffuse precipitation. Results. The aspects of changes in the immunobiochemical status of the animals in terms of age and season were determined. The findings demonstrated that with the increase in CIC in the serum of healthy animals, there was an increase in the amount of total protein, albumins, α-globulins, γ-globulins, and the number of О-cells and subpopulations of Тr- and Тs-lymphocytes. The number of β-globulins and immunocompetent cells of Т- and В-lymphocytes diminished. The animals with the asymptomatic EIA course demonstrated a reliable decrease in the fraction of albumins (р < 0.05), β-globulins (р < 0.05), and the increase in the fraction of γ-globulins (р < 0.05). In spring, healthy four-year-old and older horses had a considerable increase in the CIC rate (30.4–90.6 c.u.) as compared to other seasons (33.4–63.6 c.u.), which demonstrated the accumulation of antigen-antibody com- plexes in the organism during this period. Generally, the analysis showed that the older the horses were, the clearer the tendency towards higher CIC rate was, and the smaller the content of vitamin C with age, except for the group of 10-year-old and older horses where it was slightly increased, and there was the decrease in the lysozyme activity with age. The content of heterohemagglutinins in healthy horses increased from 6.25 to 12.02 c.u. with age, and in horses with the asymptomatic EIA course there was a decrease from 10.6 c.u. in 3-year-old horses to 6.26 in 4–9-year-old horses, and a slight increase up to 8.07 when horses were ten or more years old. The study of the seasonal state of non-specific factors of protection and humoral immunity in the selected group of horses with EIA demonstrated that the CIC rate in healthy and infected horses changed dynamically depending on the season – it was higher in spring and lower in all the other seasons. The maximal rate of CIC in infected horses was in spring (90.62 c.u.), and the minimal one – in summer (52.73 c.u.). The titer of specific antibodies to the EIA virus did not change considerably in different seasons. Conclusions. The study determined that a high CIC rate in the blood of horses with asymptomatic EIA indi- cated substantial alterations in their immunobiological status. The elevation in the rate of isoantibodies in horses with asymptomatic EIA, as compared to the healthy animals, highlighted the development of the autoimmune process in EIA-afflicted horses. This phenomenon occurred concurrently with an increase in other non-specific antibodies, contributing to an overall rise in CIC levels, while the levels of specific antibodies remained relatively stable. This study represents the first simultaneous investigation of both specific immunity (CIC) and non-specific immunity (lysozyme activity, content of vitamin C, protein fractions of blood, etc.) in the context of EIA.