II. Detection of an antigen on resting T cells down-regulated after activation

The expression of an antigen on porcine T lymphocytes detected by
murine monoclonal antibody (mAb) 8/1 was investigated by functional
studies and dual-parameter immunofluorescence. mAb 8/1 reacts with
greater than 95% of thymocytes and in peripheral blood with all T
lymphocytes and with cells of the monocyte/macrophage lineage, but
not with B cells, erythrocytes, and platelets. Pretreatment of
peripheral blood lymphocytes with mAb 8/1 plus complement abrogated
the proliferative response in vitro to mitogen, soluble antigen,
and MHC determinants. Dual-parameter immunofluorescence revealed
that resting porcine T8+ as well as T4+ lymphocytes express the 8/1
antigen, whereas after in vitro activation, cell surface expression
of the antigen was low or absent in both T cell subsets. Thus, the
8/1 antigen represents a marker that discriminates between resting
and activated T lymphocytes. Distribution and functional criteria
indicate that 8/1 represents a novel marker not described before
for any other mammalian species.