The Null/gamma delta TCR+ T cell family in the pig.

The very large population of highly thymus-dependent, non-adherent 'Null' blood lymphocytes in young pigs, which lack most surface markers characteristic of classical T-cell subsets, have recently been shown to bear several novel population- and subset-specific antigens and gamma delta T-cell receptors. These T-lymphocytes differ radically from conventional CD2-positive T-cells in their origins, biological lifespan, tissue distribution, migration behaviour, cell surface phenotype, immunological responsiveness and mechanisms of trafficking through constitutive lymphoid tissues and inflammatory lesions. Elucidation of the roles of these enigmatic cells and their characteristic surface macromolecules in the initiation and regulation of immune functions promises to reveal much of fascination.