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 130 one-day-old broiler chicks were randomly divided into four groups of 30. The groups were treated as follows: G1 included the chicks vaccinated with live F-strain MG vaccine (on eye drop of 0.03ml/dose), G2 included the chicks vaccinated with inactivated MG (0.3 ml s.c) vaccine, G3 included the chicks vaccinated with inactivated and live MG vaccines, and G4 was considered the control group, in which the chicks were not vaccinated. Blood samples were collected on days 21 and 35 of the chick's life to measure the titers of specific antibodies. On day 35, the chicks were dissected, and the bursa of Fabricius, as well as the spleen, were removed for histological evaluations. On day 21, the results showed a significant difference (P≤0.05) between all vaccinated groups in Ab titers, compared to G4, with the highest mean in G3, followed by G2 and G1, in descending order. On day 35, there was a significant difference (P≤0.05) between G3 and other vaccinated groups (G2 and G1), as well as G4. In addition, there was a significant increase in all vaccinated groups on day 35, compared to day 21. In G1, histopathological examination results showed a moderate lymphocytic hyperplasia bursal follicle. In G2, varying degrees of lymphoproliferative were observed in the major bursal follicle, and in G3, a marked lymphocytic hyperplasia bursal follicle was observed. In G4, 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 G1, and mild sinus congestion with scattered lymphocytes was recorded in the lumen in G2. In the spleen of the chicks in G3, reactive lymphoid hyperplasia was observed. In contrast to the groups mentioned above, in G4, 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.