| Abstract: | Cellular changes in spleens of mature fowl in relation to both the primary and secondary humoral antibody response following experimental EDS'76 virus infection were studied. The influence of splenectomy on humoral antibody response was also examined. Experimental fowl had been naturally infected with fowl adenovirus (FAV) but did not possess precipitins to these viruses at the time of EDS'76 virus infection. Since EDS'76 infection provokes a recall of the group antibody to FAV, this infection simultaneously induces a primary response against EDS'76 virus and a secondary response due to the recall of the group antibody to FAV. HI and precipitating antibody to EDS'76 virus (primary response) were first detected at 6 and 8 days p.i. respectively. Curves of HI, precipitating and neutralising antibody titres were biphasic; the first peak (IgM peak) occurred at 10-11 days p.i., the second (IgG peak) at 16-28 days p.i. Precipitating antibodies to FAV (secondary response) were demonstrated from 4 days p.i. The curve of these antibody titres was also biphasic, with peaks at the same times as in the primary response. Based on HI and AGP testing of primary and secondary immune response in both splenectomised and non-splenectomised fowl it is concluded that in the primary response the spleen of the adult fowl is involved significantly in only IgM secretion, while in the secondary response it is likely that both IgM and IgG are secreted in considerable amounts. Clusters of lymphoblasts and plasmablasts were observed at 3 days p.i. in the red pulp. It is very likely that antigen-antibody complexes are formed from that time and circulate bound to the surface of lymphocytes. These antigen-loaded lymphocytes are 'picked up' from the blood stream by -red pulp macrophages, leading to enhanced formation of lymphoblasts in the red pulp. Great numbers of these cells (which are very probably IgM secreting cells) were present on days 6 and 7 p.i., but were no longer detectable after day 10 p.i. -macrophages of the macrophagal ellipsoidal corona (MEC), leading to significant enlargement of the periellipsoidal lymphoid tissue (PELT) by an increase of the number of lymphocytes observed from days 4-12 p.i. The MEC was significantly enlarged from 7-12 days p.i., very likely due to an increased number of macrophages. Following deposition of antigen in the white pulp, formation of follicles begins. The number of small, intact follicles including follicle precursors increased from 6 days p.i.(ABSTRACT TRUNCATED AT 400 WORDS) |
