Phospholipase A2 (PLA2) comprises a superfamily of enzymes that hydrolyse the ester bond of phospholipids at the sn-2 position. Among the members of this superfamily, cytosolic PLA2 has attracted attention because it preferentially hydrolyses arachidonoyl phospholipids and is activated by submicromolar concentrations of Ca2+ ions and by phosphorylation by mitogen-activated protein kinases (MAP kinases). Here we investigate the function of cytosolic PLA2 in vivo by using homologous recombination to generate mice deficient in this enzyme. These mice showed a marked decrease in their production of eicosanoids and platelet-activating factor in peritoneal macrophages. Their ovalbumin-induced anaphylactic responses were significantly reduced, as was their bronchial reactivity to methacholine. Female mutant mice failed to deliver offspring, but these could be rescued by administration of a progesterone-receptor antagonist to the mother at term. Considered together with previous findings, our results indicate that cytosolic PLA2 plays a non-redundant role in allergic responses and reproductive physiology.

SummaryWe have revealed that about one and a half thousand tiny clusters, filled with one thousand closely packed lymphocytes, can be found throughout the murine small and large intestinal nmcosa. They are located in crypt lamina propria (cryptopatches; CP) and can be first detected at 14-17 d after birth. A large fraction oflymphocytes in CP expresses c-kit, IL-7R, Thyl and a lymphocyte function-associated antigen, LFA-1, whereas most of them remain CD3-, TCR oil3-, TCR "yS-, slgM-, and B220-. The population size of IL-2Ikot +, HSA + and Pgp-1 + subsets is variable (20-50%) and the composition of CD8 +, Ly-1 +, and CD4 + subsets is smaller but also variable (3-20%). In the small intestine, CP do not contain cells undergoing apoptosis nor cells bearing RAG-1 molecules, but do contain dendritic stromal cells bearing CD1 lc/CD18 molecules. The frequency of DNA replicating cells in CP is higher than that in Peyer's patches (PP), is lower than that in the thymic cortex and is almost comparable with that in the thymic medulla. The numbers of CP remain the same in aged mice (>114 wk) but double after estrogen treatment even though the thymi are attenuated sharply in both conditions. Thus, with respect to histogenesis, lymphocyte composition and tissue level of cellular behavior, neither PP, isolated lymphoid follicles, peripheral LNs, nor thymus are identical with CP. Finally, CP are virtually absent in lamina propria of IL-7R-deficient mice that display a profound reduction in thymic and peripheral lymphoid cellularity. By contrast, CP are present in germ-free mice and in athymic (nu/nu), SCID, TCR [3 • 8-/-, RAG-2 -/-, PP-deficient (aly/aly), stem cell factor (S1/S1 a) and c-kit (W/W v) mutant mice. Taking all of these results together, CP are the first identification of gut-associated murine lymphoid tissues where the generation of IL-7-dependent lympho-hematopoietic progenitors for T and/or B cell descendants may start to take place at the age of commencement of weaning.

Peyer's patch (PP) organogenesis proceeds through three histologically distinct steps: formation of organizing centers expressing VCAM-1 and ICAM-1 in segregated regions of the intestine at 15.5 days post-coitus (d.p.c.) (step I), accumulation of blood cells expressing different sets of surface markers to this region at 16.5-17.0 d.p.c. (step II), and entry of CD3+ and B220+ lymphocytes just before birth (step III). PP formation of both Il7ra-/- and Lta-/- mice is impaired from step I, suggesting involvement of the two molecules at the same timing in PP organogenesis. Expression of lymphotoxin (LT) alpha and LTbeta in IL-7 receptor (IL-7R) alpha+ cells in the intestine indicates that defects of Il7ra-/- and Lta-/- mice are due to functional inability of IL-7Ralpha+ cells in the induction of PP anlage. Blocking of IL-7Ralpha function by a single injection of the antagonistic mAb in 15.5 d.p.c. embryos suppressed appearance of VCAM-1(+) spots and expression of LTalpha and LTbeta in the intestine, which eventually resulted in mice without PP but are otherwise normal. Intestinal IL-7Ralpha+ cells are lymphoid in morphology but CD3(-) and functional in both nu/nu and Rag2-/- mice. These results implicate IL-7Ralpha+ CD3(-) cells as the direct inducer of the organizing center of PP.

The interleukin 7 receptor (IL-7R) plays a crucial role in early B-and T-cell development. It consists of a unique a chain and a common y chain [IL-2 receptor y chain (IL-2Ry)]. Gene inactivation of IL-7, IL-7R, and IL-2Ry resulted in severe impairment of B and T lymphopoiesis in mice. In addition, IL-2Ry-deficient mice lack yS T cells in the skin and have the impaired development of natural killer (NK) cells and intraepithelial lymphocytes. To explore the role of IL-7/IL-7R system in yS T-and NK-cell development, we have generated and analyzed IL-7R-deficient mice. y6 T cells were absent from skin, gut, liver, and spleen in the deficient mice. In contrast, c43 T and B cells were detected in reduced, but certain, numbers, and NK cells developed normally. The y6 T-cell development in fetal and adult thymus was also completely blocked. These results clearly demonstrate that the signal from IL-7R is indispensable for y6 T-cell development in both thymic and extrathymic pathways. On the contrary, it is suggested that NK-cell development requires cytokine(s) other than IL-7.Interleukin 7 (IL-7) is a growth factor for early B-and T-cell precursors. It was first characterized by its ability to support the growth of B-cell precursors. Subsequently, it has been shown to support survival and growth of early thymocytes and promote rearrangement of T-cell receptor (TCR) ,B and -y chains in fetal thymus and fetal liver cultures (1, 2). In vivo administration of neutralizing antibodies to IL-7 and IL-7 receptor (IL-7R) resulted in the inhibition of both B and T lymphopoiesis (3, 4). IL-7R consists of two polypeptides: a unique a chain (IL-7Ra) and a common -y chain (IL-2R 'y chain, IL-2R-y) (5, 6). IL-7R shares the IL-2R-y with the receptors for IL-2, IL-4, IL-9, and IL-15 (7 and V-y4 but not of V-y3 or V-y5 genes and sustained expression of RAG-1 and RAG-2 genes (1, 2). Collectively, these results strongly suggest that IL-7 may be also involved in the development and the maintenance of 'y6 T cells in the thymus and the periphery. Gene inactivation studies have been carried out to elucidate the in vivo function of various cytokines and their receptors. In IL-2R-y-deficient mice, numbers of T, B, and natural killer (NK) cells are reduced (15,16). In addition, DETCs are absent from the skin and the development of IELs is severely diminished. In contrast, mice deficient for IL-2, IL-4, or both cytokines have normal numbers of mature T and B cells (17, 18). On the other hand, in both IL-7-and IL-7R-deficient mice, the numbers of lymphocytes are reduced (19,20), suggesting that the impairment of T and B lymphopoiesis in IL-2Ry-deficient mice is caused by depletion of the signal by IL-7. However, studies have not been reported on the development of y8 T and NK cells in IL-7R-deficient mice.To elucidate the role of IL-7/IL-7R system in y8 T-cell development, we have generated and analyzed IL-7R-deficient mice. yS T cells were absent from these mice, while decreased, but certain, numbers of mature af3 T cells were detected. ...