Igor Dozmorov

Limiting dilution analysis: from frequencies to cellular interactions

Abstract Molecular biology techniques have provided the means to pursue the precise definition of molecular components in a single cell type and its clonal progeny. However, to study the workings of the individual components of the immune system as well as the system itself, additional tools and supplementary approaches are required.

Age-associated decline in responses of naïve T cells to in vitro immunization reflects shift in glucocorticoid sensitivity.

Naïve T lymphocytes from young mice can be immunized to protein antigens in vitro if the initial exposure to antigen is followed by a brief period of clonal expansion in the presence of both the glucocorticoid dexamethasone (at 10(-8) M) and antibodies to Interleukin-10 (IL-10). These cultures produce cell lines that respond to antigen rechallenge by proliferation and cytokine secretion. T cells from older mice, however, do not respond under these conditions unless the dexamethasone concentration is raised to levels (10(-7) M) that are inhibitory for T cells of young mice. Suitably timed exposure to dexamethasone can also increase proliferative responses to polyclonal activation via the CD3 component of the T cell receptor, and again optimal responses are obtained from old mice only at steroid concentrations that are super-optimal for young T cells. Diminished sensitivity to glucocorticoid effects may contribute to the poor responses of aged mice to novel immunogens.