A critical role of T-cell receptor gamma/delta cells in antibacterial protection in mice early in life

Although it is generally assumed that T-cell receptor (TCR) gamma/delta cel ls participate in protection against intracellular microbial pathogens, the ir impact remains controversial. In our study, young (14-day-old) mice lack ing TCR gamma/delta cells were far more susceptible to Listeria monocytogen es than mild-type (WT) mice of the same age. The number of interferon gamma (IFN-gamma) producers responsible for antilisterial resistance was signifi cantly higher among natural killer (NK)1(+) TCR gamma/delta cells than amon g NK1(-) TCR gamma/delta cells. Endogenous IFN-gamma neutralization increas ed susceptibility of young WT mice to L. monocytogenes infection. Liver was a major residence of peripheral NK1(+) TCR gamma/delta cells, whereas NK1( -) TCR gamma/delta cells were broadly distributed in various lymphoid organ s. Numbers of both NK1(+) and NK1(-) TCR gamma/delta cells increased in the liver of WT mice prior to TCR alpha/beta cells and represented a substanti al population in early life (14 days after birth). Virtually all NK1(+) TCR gamma/delta cells expressed activation markers, whereas substantial number s of NK1(-) TCR gamma/delta cells showed a naive phenotype. We conclude tha t TCR gamma/delta cells play a critical role in protection against L. monoc ytogenes in the early life of mice, probably because their TCR alpha/beta c ell compartment is not fully competent. For this antibacterial function, we assign NK1(+) TCR gamma/delta cells a more important role than their NK1(- ) cognates.