Gene expression profiling was used to compare the gene expression
patterns of human germinal center (GC) T helper (Th) cells with
other CD4+ T-cell subsets (naive, central, and effector memory
T cells). GC-Th cells, specifically localized in germinal centers
to help B cells, are distantly related to central and effector
memory T cells in global gene expression profiles. GC-Th cells
displayed substantial differences in mRNA for adhesion molecules,
chemoattractant receptors, and cytokines compared with other populations.
Distinct expression of transcriptional factors by GC-Th cells
is consistent with the hypothesis that they may be different from
other T cells in cell lineage. Interestingly, CXCL13, a critical
chemokine for B-cell entry to lymphoid follicles, is one of the
most highly up-regulated genes in GC-Th cells. GC-Th cells (but
not other T cells) produce and secrete large amounts of functional
CXCL13 upon T-cell receptor activation, a process that is dependent
on costimulation, requires translation and transcription, and
is dramatically enhanced by activation in the presence of GC-B
cells. This study revealed for the first time the unique gene
expression program of GC-Th cells.