Abstract
Granulocytes of the epigonal and Leydig organs of Rhizoprionodon lalandii were identified and classified into three different cell types, type I and type II eosinophils and neutrophils. The development of these cells in the haematopoietic tissues was dynamic, demonstrated by nuclear immunopositivity for the proliferating cell nuclear antigen (PCNA) proteins and was regulated by various cytokines, including the transforming growth factor β ‐l (TGF/ β 1 ). The expression pattern of these cells was heterogeneous among individual cells and TGF/ β 1 ‐immunostaining was found principally in the cytoplasm of immature granulocytes. The presence of TGF/ β 1 in cells about to divide was demonstrated suggesting that modulation of differentiation and proliferation occurs in the haematopoietic tissues of this species of elasmobranch.