J. Ismaili et al., CD4 AND CD8 EXPRESSION AND T-CELL ANTIGEN RECEPTOR GENE REARRANGEMENTIN EARLY INTRATHYMIC PRECURSOR CELLS, European Journal of Immunology, 26(4), 1996, pp. 731-737
The earliest T precursor population in the adult mouse thymus, conside
red to have the surface phenotype CD4(lo)8(-)3(-)44(-)Thy-1(lo) c-kit (termed the low CD4 precursor), has been shown to have the capacity t
o produce B cells and dendritic cells, as well as T cells, and to hove
the T cell antigen receptor (TCR) C beta, gene region in germ-line co
nfiguration. Because of evidence that this precursor population may ha
ve low levels of CDS as well as CD4 on the cell surface, it nas isolat
ed, stained for surface CD4 and CD8 and assayed For the expression of
messenger RNA (mRNA) for CD4 and CDS by the reverse transcriptase poly
merase chain reaction (RT-PCR). The low CD4 precursors gave definite,
moderate levels of staining for both CD8 and CD4. in contrast to downs
tream precursors which showed only marginal staining and so could be c
onsidered as genuine CD4(-)8(-)3(-) triple negatives. The low CD4 prec
ursor expressed a significant level of mRNA for CD4, indicating that t
he surface C4 was produced by these cells. However. the low CD4 precur
sor did nor express a detectable level of mRNA for CDS. suggesting tha
t the surface CDS was acquired from other cells. Since the lon CD4 pre
cursor population was found already to express mRNA fur enzymes involv
ed in TCR gene rearrangement, including in this study terminal deoxynu
cleotidyl transferase (TdT). a PCR procedure was used to assay early p
recursors for D-J rearrangements at the TCR beta gene locus. However.
the low CD4 precursor had the TCR beta D-J genes in germ-line configur
ation, D-J gene rearrangements being first detected several stages dow
nstream in the CD3(-)4(-)8(-)44(-)25(-) precursor population. We concl
ude that a transient synthesis of CD4, but not of CD8. characterizes t
hese early thymus precursors. Although they have initiated synthesis o
f some recombination-associated enzymes. full commitment to the T line
age and TCR gene rearrangement is a later event.