Blood, 15 January 2002, Vol. 99, No. 2, pp. 531-537
IMMUNOBIOLOGY
Expression of the recombination-activating genes in
extrafollicular lymphocytes but no apparent reinduction in germinal
center reactions in human tonsils
Nadine Meru,
Andreas Jung,
Irith Baumann, and
Gerald Niedobitek
From the Pathologisches Institut,
Friedrich-Alexander-Universität, Erlangen, Germany.
V(D)J recombination in lymphocytes is mediated by 2 recombination-activating genes, RAG1 and RAG2,
which are expressed during lymphocyte development in bone
marrow and thymus. Prompted by studies reporting re-expression of the
RAGs in germinal center B cells, the expression of RAGs and terminal
deoxynucleotidyl transferase (TdT) in human lymphoid tissues was
examined using in situ hybridization and immunohistochemistry,
respectively. Here it is shown that RAGs and TdT are not
reinduced in germinal center reactions. However,
RAG+/TdT+ cells are frequently present in
extrafollicular areas of tonsils mainly at the boundary between
lymphoid tissue and fibrous scaffold. Phenotypic analyses suggest that
these cells are B cells. Finally, it is shown that
RAG+/TdT+ cells are found more frequently in
tonsils than in other peripheral lymphoid tissues. This may reflect an
increased influx of RAG+/TdT+ cells as a result
of higher antigenic stimulation at this site. Alternatively, this
observation may indicate that the tonsils are an additional site of
lymphocyte ontogeny.
