In brief

Allergy

Basophils orchestrate chronic allergic dermatitis and protective immunity against helminths Ohnmacht, C. et al. Immunity 1 Sep 2010 (doi:10.1016/j.immuni.2010.08.011)

CD11c depletion severely disrupts Th2 induction and development in vivo Phythian-Adams, A. T. et al. J. Exp. Med. 6 Sep 2010 (doi:10.1084/jem.20100734)

Inflammatory dendritic cells — not basophils — are necessary and sufficient for induction of Th2 immunity to inhaled house dust mite allergen Hammad, H. et al. J. Exp. Med. 7 Sep 2010 (doi:10.1084/jem.20101563)

Basophils have recently attracted much interest as an antigen-presenting population, but the overall importance of basophils for T helper 2 (T_H2)-type immunity has remained unclear. These new studies suggest that only dendritic cells (DCs) are crucial for the initiation of T_H2-type immunity; basophils instead seem to be important for promoting chronic and secondary T_H2-type responses. Ohnmacht et al. generated a transgenic mouse that constitutively lacked most basophils; these mice had normal T_H2 cell responses to allergens and the helminth Nippostrongylus brasiliensis but showed resistance to IgE-dependent chronic allergic dermatitis and increased susceptibility to secondary helminth infections. However, DC-depleted mice had defective T_H2 cell development following immunization, despite normal basophil recruitment. Similarly, Phythian-Adams et al. reported that although DC depletion inhibited T_H2 cell development following infection with Schistosoma mansoni, depletion of basophils had no effect. Hammad et al. showed that only DCs were essential for T_H2 cell responses to house dust mite allergen. High-affinity Fc receptor for IgE (FcεR1)⁺ inflammatory DCs, but not basophils, presented antigen and induced T_H2 cell development following exposure to allergen. However, basophils did amplify the T_H2-type response following allergen challenge. The description of a role for FcεR1⁺ DCs may explain why previous studies using FcεR1-specific antibodies to deplete basophils suggested that they were crucial for T_H2 cell development.

T cell responses

Responses against a subdominant CD8⁺ T cell epitope protect against immunopathology caused by a dominant epitope Ruckwardt, T. J. et al. J. Immunol. 10 Sep 2010 (doi:10.4049/jimmunol.1001606)

The CD8⁺ T cell response to respiratory syncytial virus (RSV) in CB6F1 mice is focused on two viral epitopes — the immunodominant epitope H2-K^d–M2_82–90 and the subdominant epitope H2-D^b–M_187–195. Although RSV is cleared efficiently by the T cell response, this often results in immunopathology; this study looked at the contribution of these viral epitopes to immunity versus host damage. By mutating MHC-binding anchor residues in the RSV M2 and M proteins, the authors could study the responses to M2_82–90 and M_187–195 separately. Absence of the dominant M2_82–90 epitope was compensated for by an increased response to the subdominant M_187–195 epitope; this increased response effectively cleared RSV and resulted in less illness. Absence of M_187–195 resulted in 'overcompensation' by the response to M2_82–90 and increased illness that correlated with decreased functionality of the dominant T cell population as measured by cytokine production. These results indicate that the subdominant H2-D^b–M_187–195 response exerts some form of beneficial control over the dominant H2-K^d–M2_82–90 response.