Allergy

The absence of interleukin 9 affects neither the development of allergen-induced pulmonary inflammation nor airway hyper-reactivity. McMillan, S. J. et al. J. Exp. Med. 195, 51–57 (2002) [PubMed].

The TH2-derived cytokine IL-9 has been implicated in the development of asthma. McMillan et al. investigated the effect of IL-9 deficiency on the development of asthma and airway hyper-reactivity (AHR) after allergen challenge. AHR and eosinophilia occurred to a similar degree in Il9−/− mice and wild-type mice, and goblet cell hyperplasia and immunoglobulin E production were also unaffected in the absence of IL-9. IL-9 is therefore not obligatory for asthma development.

T-cell homeostasis

Homeostatic competition between T cells revealed by conditional inactivation of the mouse Cd4 gene. Wang, Q. et al. J. Exp. Med. 194, 1721–1730 (2002) [PubMed].

The role of T-cell receptor (TCR) signalling in T-cell homeostasis and post-thymic selection of naive T cells is unknown. Here, Wang et al. report the impairment of TCR signalling by conditionally inactivating expression of the co-receptor CD4 and the effects this has on homeostatic events. They show that T cells compete with each other during homeostatic proliferation and that T cells lacking CD4 compete poorly, indicating that the competition is based on the strength of TCR signal the cells receive.

Haematopoiesis

Identification of the earliest prethymic bipotent T/NK progenitor in murine foetal liver. Douagi, I. et al. Blood 99, 463–471 (2002) [PubMed].

Douagi et al. describe the identification of a novel population of common T/NK cell progenitors (C-TNKPs) within the foetal liver. These cells are proposed to represent the immediate developmental step before migration to the thymus. This population of B220loc-kit+CD19− cells, which compose 0.2% of foetal liver cells, represent 70% of T-cell precursors in the foetal liver. These cells can produce both T- and NK-cell progeny at the single cell level and are present in athymic mice, indicating their prethymic origin.

Immune regulation

IL-10-producing CD4+ T cells mediate tumour rejection. Segal, B. M., Glass, D. B. & Shevach, E. M. J. Exp. Med. 168, 1–4 (2002) [PubMed].

Although IL-10 is typically thought to have immunosuppressive functions, Segal et al. describe a pro-inflammatory population of IL-10-producing CD4+ T cells that mediate anti-tumour immunity. In a subcutaneous model of glioma cell growth, IL-10-producing CD4+ T cells that were crucial for tumour rejection were generated after vaccination with irradiated glioma cells. The cells had a cytokine profile resembling the immunoregulatory TR1 cells that can be generated in vivo in the presence of IL-10.