Significance of unconventional peripheral CD4+CD8dim T cell subsets.

Routine T cells phenotyping occasionally reveals a CD4+CD8dim T cell subset with an apparently homogeneous dot plot. The aim of this study was to elucidate their immunological significance from analysis of 31 healthy donors, 21 elderly and 220 immune deficient patients. CD4+CD8dim T cells expressed reduced levels of CD8 (11-17,000 compared to 96-128,000 mol/cell on CD8+ T Cells). CD4 was expressed at the same level as on CD4+ T cells. The occurrence of raised CD4+CD8dim T cells (> 20 cells/muL) was similar in kidney transplant recipients (28.4%) and healthy donors (26%). It was somewhat lower in HIV+ patients (19.7%) possibly due to virally induced CD4+ T lymphopenia. However, an age effect is possible because the occurrence was raised (33.3%) in 70 volunteers (chi2 test NS). On the other hand, the size of the CD4+CD8dim subset was not correlated with age. CD4+CD8dim T cells did not express the activation markers CD69 (n = 220) or CD25 (n = 10) and expressed the homodimeric (alphaalpha) isoform of CD8, suggesting they are related to mucosal immunity (MALT). We selected 29 patients with unambiguous dot plots. In 26 of them one predominant TCR Vbeta clonotype was expressed on 18 to 94% of CD4+CD8dim T cells and never on more than 10% of conventional T cells. The predominant clonotypes were Vbeta8 (n = 5), Vbeta2 (n = 4), Vbeta13.1 and Vbeta 21 (n = 3 each). Whether this reveals a chronic stimulation or an emerging lymphoproliferative disorder must be elucidated. We propose to name this entity: "Oligoclonal Clonopathy of Undetermined Significance (OCUS)."