LD1: a CD4-CD8- TCR alpha beta/CD3+ peripheral T cell line with helper function for B lymphocytes

In order to learn more about the small subset of CD4-CD8- TCR alpha beta/CD3+ peripheral T lymphocytes, we firstly characterized at the cellular and molecular levels the CD4-CD8- LD1 cell line isolated from the spleen of an MRL/lpr-lpr mouse. Secondly we studied its functional properties. LD1 cells are Thy1+ CD5+ CD4-CD8- LFA-1+ PgP-1+ and do not bind the T cell precursor-specific antibodies Joro 37-5 or Joro 75. They are negative for IgM, B-220, BP-1, J11d, Lyb8, Ia, F4/80, BP-2, and Mac-1 surface markers. LD1 cells have deleted the TCR delta locus, have rearrangements at the TCR gamma gene cluster (i.e. a V gamma 1-J gamma 1-C gamma 1 and a V gamma 4.3-J gamma 4-C gamma 4) and have two rearrangements of the TCR beta gene cluster (i.e. a D beta 1-J beta 1 and V-D-J beta 2). LD1 cells produce normal sized RNA transcripts from TCR alpha and beta genes and lower levels of gamma-mRNA. These cells bind CD3- and pan-TCR beta-specific antibodies as determined by FM analysis. We conclude that LD1 cells bear a TCR alpha beta/CD3 type of receptor complex. LD1 cells fail both in vivo and in vitro to differentiate into CD4+ or CD8+ cells. These cells help B lymphocytes to mature into antibody-secreting cells, secrete IL-3 and IL-6 but not IL-2, IL-4, or IL-5, and exert no detectable cytolytic activity. These results together with recent reports of antigen-specific CD4-CD8- TCR alpha beta/CD3+ cytotoxic T cell lines show that the CD4-CD8- TCR alpha beta/CD3+ subset comprises functionally competent helper and cytotoxic T lymphocytes and thereby argue for their potential to participate in immune responses. Our results also suggest that cells like LD1 represent terminally differentiated T lymphocytes rather than cells with precursor potential for CD4+ or CD8+ TCR alpha beta/CD3+ T lymphocytes.