SPONTANEOUS AND STIMULATED CHEMILUMINESCENCE RESPONSES OF BLOOD LEUKOCYTES FROM HEALTHY AND INFECTED TILAPIA

A bimodal distribution in the spontaneous chemiluminescence (SpCL) mea surements in naive tilapia leads us to divide the fish into low and hi gh responder groups. Because of the homogeneity in both differential p hagocyte cell counts and stimulation indexes, it is suggested that dif ferences between the responder groups are due to innate intrinsic fact ors. Difference between these two groups is also displayed, in a less significant manner, in zymosan stimulated chemiluminescence (zStCL) th at showed a weak linear regression factor (R-2=0.4756). In naive tilap ia, Streptococcus difficile bacterin-stimulated chemiluminescence (bSt CL) values were much lower than those obtained in zStCL. When sibling fish were infected with live S. difficile bacteria, a spectacular incr ease in bStCL values, with a high stimulation index of 42, was display ed on day 6 after infection. The SpCL and bStCL values increased consi derably in diseased fish which displayed a serious symptomatology on d ay 36 after infection. However, fish that developed resistance to the disease showed lowe red values in both SpCL and bStCL. The implication of these findings in the in vivo production of reactive oxygen radica ls by phagocytic cells and their connection to resistance and suscepti bility to disease are discussed in comparison to mammals.