Age-related changes of the antigen-specific antibody formation in vitro and PHA-induced T-cell proliferation in individuals who met the health criteria of the Senieur protocol.

The antigen-specific antibody secretion in vitro after immunisation with the primary T-cell dependent antigen Helix pomatia Haemocyanin (HPH) was investigated in both young and elderly individuals, who all met the health admission criteria for immunogerontological studies as detailed in the SENIEUR protocol. In addition, elderly non-Senieur persons were incorporated in this study. Young and elderly Senieur volunteers were fully comparable in terms of the occurrence of anti-HPH antibody secreting cells after in vitro simulation of peripheral blood mononuclear cells with variable doses of the antigen. In contrast, the non-Senieur elderly showed a lower number of anti-HPH antibody secreting cells in vitro. PHA-conditioned medium did enhance this in vitro response, whereas the addition of IL-2 remained ineffective. The PHA-induced T-cell proliferation was found to be somewhat impaired in elderly Senieur individuals and significantly lower in elderly non-Senieur individuals compared to young healthy persons. Using an immunofluorescence double staining technique after BrdU incorporation, the phenotype of the proliferating cells was determined. Again the total number of proliferating cells was impaired in the non-Senieur elderly. No changes in the relative contribution of CD4+ or CD8+ cells to the number of proliferating cells were found in the different age groups. On the other hand, a significantly lower number of proliferating cells with IL-2 receptor expression were detected in the non-Senieur individuals, which could account for the lack of response to IL-2 in this group. Our study clearly shows that so-called age-associated immune deficiency can be the result of disease and not necessarily of the ageing process itself.

Expression of the transcription factor GATA-3 is required for the development of the earliest T cell progenitors and correlates with stages of cellular proliferation in the thymus.

GATA-3 is a zinc-finger transcription factor that is essential for both early T cell development and Th2 cell differentiation. To quantify GATA-3 expression during T cell development in vivo in the mouse, the GATA-3 gene was targeted by insertion of a lacZ reporter by homologous recombination in embryonic stem (ES) cells. Although we could detect GATA-3+ cells throughout T cell development in the thymus, the proportions of GATA-3+ cells varied considerably between the distinct differentiation stages. The two periods of TCR alpha and beta gene recombination, which occur in quiescent or slowly dividing cells, were associated with low proportions of GATA-3+ cells. Conversely, the stage of rapidly proliferating cells, which insulates these two waves of TCR rearrangement, was characterized by a large proportion of GATA-3+ cells. In addition, we generated chimeric mice by injection of GATA-3-deficient, lacZ-expressing ES cells into wild-type blastocysts. In this in vivo competition analysis, no contribution of GATA-3-deficient cells to the T cell lineage was detected, not even in the earliest CD44+CD25- double-negative (CD4-CD8-) cell stage in the thymus. These results parallel data implicating other GATA family members as key regulators of proliferation and survival of early hematopoietic cells. We therefore propose that GATA-3 is required for the expansion of T cell progenitors, and for the control of subsequent proliferation steps, which alternate periods of TCR recombination in the thymus.