Ultrastructure of Circulating Lymphocytes in Thymus Disorders

Abstract

Extract: Peripheral blood lymphocytes of normal children, children with viral infections, and children with congenital thymic disorders were examined by electron microscopy. Lymphoid cells were classified as small or medium lymphocytes, lymphoblasts, plasmablasts, or plasma cells by certain morphological criteria. Enumeration and classification of cells in normal children revealed that 73.4% were small lymphocytes and 26.6% were medium lymphocytes. No lymphoblasts, plasmablasts, or plasma cells were found in peripheral blood of normal children. In children with infections or congenital thymic disorders, small but significant numbers of lymphoblasts, plasmablasts, and plasma cells were found. Medium lymphocytes were twice as numerous as small lymphocytes. In congenital thymic disorders, there was an absolute depletion of small lymphocytes, whereas medium lymphocytes and more immature forms were present in normal numbers in peripheral blood. Speculation: The absence of thymus-dependent immunological function is correlated with a deficit in small lymphocytes. This may be due to an absence of the bone marrow precursors of these cells or to a lack of thymic influence on a cell type which remains unidentified.