Immune response of the harderian gland in chickens to infectious bronchitis coronavirus

Aim. To determine the difference in immune responses of the harderian gland in clinically healthy chickens and the ones with infectious bronchitis based on the content, localization and morphometric estimation of the surface markers of Т- and В-lymphocytes and to determine the differentiation index as an indicator of assessing body defenses. Methods. Histological, immunohistochemical, optical, morphometric and statistical. Results. The histological study of the harderian gland of chickens with infectious bronchitis determined the swelling and proliferation of the connective tissue as well as infiltration of secretory lobules by lymphoid cells. It was found that the immunity of chickens with infectious bronchitis, in which the harderian gland plays a relevant role, depends considerably on the differentiation index of immunocompetent cells. There was a reliable 1.77- and 1.36-fold decrease in this indicator for 40- and 90-day-old chickens, respectively, in case of nephroso-nephritic form of infectious bronchitis which demonstrated a weaker function of the defense cells of this organ. According to the cytomorphometric analysis, the number of cells, expressing CD4+, CD8+, CD20+, CD45RA+ markers in the harderian gland of sick 20-, 40-, and 90-day-old chickens with respiratory and nephroso-nephritic forms of infectious bronchitis was reliably (P < 0.05) increasing compared to the clinically healthy chickens. For instance, the number of mature В-lymphocytes increased in sick 20-day-old chickens – 2.44 times, 40-day-old chickens – 1.88 times, and 90-day-old ones – 2.62 times compared to clinically healthy chickens. Conclusions. The data were obtained about the changes in quantitative and qualitative composition of lymphocytes with surface markers CD4+, CD8+, CD20+, CD45RA+ in the harderian gland of chickens with infectious bronchitis. Our results will supplement current knowledge about the feasibility of immunohistochemical methods in the diagnostics of avian infectious bronchitis.