Control of Lymphocyte Growth in Response to Phytohemgglutinin Stimulation

Abstract

Circulating lymphocytes under appropriate stimulation transform into large proliferating blast cells in a predictable fashion. When compared to resting lymphocytes, the proliferating blast cells can be distinguished morphologically by their large size, open, finely textured nuclear chromatin, prominent nucleoli and copious cytoplasm abounding with ribosomes clusters (l). These characteristics reflect heightened metabolic activities such as increased RNA and protein synthesis (2). We have previously demonstrated that phytohemagglutinin (PHA) induced enlargement of resting lymphocytes into proliferating blast cells is accompanied by an early increase in the synthesis and utilization of ribosomal RNA (rRNA) (3). Presumably this new rRNA provides for the delivery of additional cytoplasmic ribosomes and secondarily increased protein synthesis which ultimately culminates in lymphocyte growth and the morphologic appearance of a blast.

Supported in part by USPHS Grant CA 10478 from the National Cancer Institute and Contract AT(30-1)3833 from the Atomic Energy Commission and by the Albert A. List, Frederick Machlin and Anna Ruth Lowenberg funds.