Cell division-associated expression of an epitope, KH17, on early developing thymocytes

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Abstract
A newly established monocional antibody, KH17, detects a unique epitope temporarily expressed on early developing CD3− thymocytes confined to a cycling stage. KH17 is detectable on a part of CD4−CD8−, CD4−CD8+, and CD4+CD8+ cells, but not on CD4+CD8− thymocytes. By four-color flow cytometry analysis using KH17, we were able to define the heterogeneity of immature CD4−CD8− thymocytes by the expression of KH17 and IL-2R. In Thy-1-congeneic bone marrow chimeras, the appearance of KH17-IL-2R+ thymocytes preceded the increase of KH17+ IL-2R− cells. The antibody could also divide CD3−CD4−CD8+ cells into two subpopulations, KH17+ and KH17−, which showed a continuum. In the fetal thymus there was a rapid and dramatic increase of KH17−CD4+CD8+ thymocytes concomitant with a decrease of KH17+CD4−CD8+ thymocytes in later gestation days. KH17 is not expressed on resting peripheral T cells, but is expressed on a large proportion of Con A-activated blastic spleen cells. The KH17 molecules precipitated from Con A-activated spleen cells were 55 and 75 kd polypeptides, but different from IL-2R subunits.