PREVALENCE AND ACTIVATION PHENOTYPE OF SENDAI VIRUS-SPECIFIC CD4(-CELLS() T)

The relative prevalence of Sendai virus-specific CD4(+) T helper precu rsors (Thp) has been assessed by limiting dilution analysis (LDA). Wit hin 10 days after intranasal inoculation of C57BL/6 mice, Thp prevalen ce increased from <1 in 10(5) to approximately 1 in 200 in CD4(+) T-ce ll-enriched spleen and mediastinal lymph node populations. These frequ encies remained elevated relative to naive animals, with the majority of the Thp recovered at 2-3 months after infection being found in the spleen. The ''memory'' Thp express an ''activated'' L-selectin-low, CD 44-high, alpha 4-integrin-high phenotype, comparable to that described previously for CD8(+) cytotoxic T lymphocyte precursors (CTLp) specif ic for Sendai virus. Background effects for the IL-2-based Thp analysi s are, however, less predictable than those round previously for the C r-51 release CTLp LDA, as the extent of non-virus-specific lymphokine production varies. However, provided the analysis is appropriately con trolled, the approach does allow useful comparisons between phenotypic ally different subsets of antigen-specific CD4(+) T cells. (C) 1995 Ac ademic Press, Inc.