PNA lectin-based separation of thymocytes into mature and immature subpopulations: CD4-8- double negative cells display characteristics of PNAlo mature thymocytes.

Cortical (immature) thymocytes are widely reported to express intermediate to high levels of receptors for the lectin, peanut agglutinin (PNA). Light-scatter studies of murine fetal thymocytes stained with PNA or anti-mouse CD4 and CD8 monoclonal antibodies indicated, however, that the most immature CD4-8- (DN) thymocyte subpopulation binds levels of PNA commonly described as PNAlo. Evaluation of the PNA binding characteristics of fetal thymocytes negative for the CD8 antigen confirmed the existence of a major population (approximately 20% of total cells) of CD4-8- PNAlo fetal thymocytes. The majority of these DN thymocytes were subsequently found to bind sub-agglutinating levels of PNA, similar to mature CD4+ or CD8+ single positive (SP) thymocytes. Given this information, an immunomodulating compound (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) known to produce a maturational delay in murine thymocytes was tested for a possible concurrent effect on thymocyte PNA lectin binding. A TCDD-induced increase in DN thymocytes was found to be paralleled by an increase of equal magnitude in PNAlo thymocytes. Taken together, these data provide evidence that acquisition of the PNA receptor may be a maturational event occurring during the DN stage of thymocyte ontogeny. Further, these results suggest that separation of thymocytes into mature (medullary) and immature (cortical) subpopulations by PNA agglutination may result in contamination of medullary cells by the most immature (DN) subpopulation of thymocytes.