Immune Response and Histological Changes in Broilers Chickens Vaccinated with Mycoplasma gallisepticum Vaccines

Mycoplasma is unique among prokaryotes because of its small size, small genomes, and complete lack of cell walls, which makes them cell wall-less prokaryotes. This study aimed to evaluate the effect of vaccinating one-day-old chicks with inactivated and live vaccines (CRDF) of Mycoplasma gallisepticum (MG) on their humoral immune response and immune organs. The Enzyme-Linked Immunosorbent Assay was used to measure Ab titers and investigate histopathological changes. A total of ۱۳۰ one-day-old broiler chicks were randomly divided into four groups of ۳۰. The groups were treated as follows: G۱ included the chicks vaccinated with live F-strain MG vaccine (on eye drop of ۰.۰۳ml/dose), G۲ included the chicks vaccinated with inactivated MG (۰.۳ ml s.c) vaccine, G۳ included the chicks vaccinated with inactivated and live MG vaccines, and G۴ was considered the control group, in which the chicks were not vaccinated. Blood samples were collected on days ۲۱ and ۳۵ of the chick’s life to measure the titers of specific antibodies. On day ۳۵, the chicks were dissected, and the bursa of Fabricius, as well as the spleen, were removed for histological evaluations. On day ۲۱, the results showed a significant difference (P≤۰.۰۵) between all vaccinated groups in Ab titers, compared to G۴, with the highest mean in G۳, followed by G۲ and G۱, in descending order. On day ۳۵, there was a significant difference (P≤۰.۰۵) between G۳ and other vaccinated groups (G۲ and G۱), as well as G۴. In addition, there was a significant increase in all vaccinated groups on day ۳۵, compared to day ۲۱. In G۱, histopathological examination results showed a moderate lymphocytic hyperplasia bursal follicle. In G۲, varying degrees of lymphoproliferative were observed in the major bursal follicle, and in G۳, a marked lymphocytic hyperplasia bursal follicle was observed. In G۴, on the other hand, no obvious histopathological findings were recorded. The results of the spleen histopathological evaluation showed various degrees of lymphoproliferative and moderate neutrophilic infiltrate in the red pulp in G۱, and mild sinus congestion with scattered lymphocytes was recorded in the lumen in G۲. In the spleen of the chicks in G۳, reactive lymphoid hyperplasia was observed. In contrast to the groups mentioned above, in G۴, the spleen structure showed a typical structure. It was concluded that the chicks vaccinated with inactivated and live MG vaccines experienced increased production of Ab titers and the immune stimulation of immune organs.

Keywords:

Mycoplasma gallisepticum , Live vaccines , vaccine