ABSTRACT
Apoptosis [programmed cell death] is an important mechanism for preservation of a healthy and balanced immune system in vertebrates. Little is known, however, about how apoptosis processes regulate invertebrate immune system. Thus, the present histopathological study was performed to search for the level of apoptosis on hemocytes of three bivalve species namely, Macoma edentula, Hiatula rupelliana and Gastrana fraglis in the Timsah Lake infected with branchial Rickettsia-like parasites and ciliated parasites in the digestive gland. Microscopically, special to elongated intracytoplasmic Rickettsia-like colonies were observed in the base of gill filaments of the clams. Histologically, the distribution and shapes of apoptotic cells were classified into three main types. The aggregation of apoptotic cells were observed in the apical and the basal parts of the ciliated cells lining the gill epithelium. These results provide a first insight into apoptotic processes in mollusc immune cells