Caspase recruitment domain-containing membrane-associated guanylate kinase protein-1 (CARMA1) is a kinase that is phosphorylated upon TCR engagement and thought to amplify TCR signaling during T cell activation. Ramadas et al. (p. 6197) used a conditional CARMA1 mutant mouse strain to study how CARMA1 expression affects memory T cell responses. Mice expressing floxed CARMA1 were crossed with mice that expressed Cre recombinase under the OX40 promoter to generate a strain, OX40+/CreCARMA1F/F, in which CARMA1 was conditionally deleted upon OX40 expression after T cell activation. CD4+ T cells from OX40+/CreCARMA1F/F mice showed impaired reactivation and reduced NF-κB signaling in vitro compared with CD4+ T cells from OX40+/+CARMA1F/F control mice. Allergic airway inflammation, as well as eosinophil infiltration and Th2 cytokine expression in the lungs, were reduced in CARMA1-defienct mice upon Ag rechallenge relative to control mice. Memory T cell responses were not compromised upon rechallenge in OX40+/CreCARMA1F/F mice. In contrast, Ag rechallenge of wild-type mice after adoptive transfer of Th2-polarized CD4+ T cells from OX40+/CreCARMA1F/F mice caused significantly less airway inflammation relative to mice given Th2-polarized wild-type cells. These data reveal that CARMA1 influences both effector and memory T cell responses during reactivation and may be a potential target for asthma treatment.

Access to Tcrb loci is tightly regulated during Vβ-to-DJβ recombination in double-positive (DP) thymocytes to ensure allelic exclusion. Kondilis-Mangum et al. (p. 6374) developed novel TCR transgenic alleles to better define the underlying mechanisms required for feedback inhibition of recombination and consequent allelic exclusion. They analyzed recombination between two alleles that were both designed to maintain chromatin accessibility, but only one allele brought the Vβ and DJβ segments in physical proximity. This comparison revealed that physical proximity did promote recombination and could overcome feedback inhibition. Another allele confirmed that gene accessibility was essential to recombination, as segments in physical proximity were still affected by feedback inhibition if the chromatin was inaccessible. These results provide evidence that locus accessibility and gene segment proximity have a significant effect on the enforcement of allelic exclusion during thymocyte development.

NK cell specificity is regulated by the integration of activating and inhibitory signals that allow NK cells to attack infected or tumor cells without harming nonthreatening self cells. In humans, the CD94/NKG2A heterodimer functions as an inhibitory receptor, whereas CD94/NKG2C activates NK cells. Saether et al. (p. 6365) examined the sequences of CD94 and NKG2A, -C, and -E in the mouse and rat and observed functional differences compared with the human heterodimers. The mouse and rat CD94 sequences include a lysine residue within the transmembrane domain, which is not found in the human sequence. In addition, between the stalk and transmembrane domains, the mouse and rat NKG2C and -E sequences have an arginine residue in place of the lysine residue normally seen in human NKG2C and -E that is known to be required for interactions with the activating adaptor proteins DAP12 and DAP10. The rat CD94/NKG2C heterodimer was able to interact independently with DAP12 and DAP10 to activate NK cell cytoxicity, but this interaction was mediated instead through the lysine residue in the transmembrane domain of CD94. These results highlight how different variations of NKG2C/E and CD94 in the mouse and rat preserve their activating function as a heterodimer, confirming the importance of these receptors’ activity in NK cell function.

Rhesus macaques expressing Mamu-B*17 MHC class I (MHC I) molecules have been shown to better control replication of simian immunodeficiency virus (SIV) relative to other MHC I alleles. The mechanism by which Mamu-B*17-mediated presentation of SIV peptides affects replication is not well understood. Wu et al. (p. 6382) studied the crystal structures of Mamu-B*17 in complex with eight different immunodominant peptides from SIVmac239 to better understand how this MHC I molecule influences viral replication. The peptides were 8–11 aa in length, and their aa sequences varied widely. Similar to other MHC I molecules, pocket B and pocket F of Mamu-B*17 formed the key peptide anchor sites. Pocket B could bind to a variety of N-terminal anchor residues with different side chains that occupied positions P1, P2, or P3 of the peptide. The binding specificity of pocket F was more stringent, such that only residues with aromatic side chains could serve as C-terminal anchor residues. The Mamu-B*17 binding groove appeared to be highly flexible in that it accommodated residues of different specificities and allowed them to assume diverse conformations. This flexibility also facilitated presentation of different TCR contact residues, thus suggesting that Mamu-B*17 may be able to facilitate crossreactive TCR responses. These observations reveal new structural perspectives on how Mamu-B*17 interactions with SIV peptides may impact immune responses.

Talin1 is a linker molecule that can interact with both integrins, including LFA-1, and cytoskeletal components. Talin1 has been found in supramolecular activation clusters in T cells during immunological synapse formation with APCs. To better understand the role of talin1 in T cell–APC interactions, Wernimont et al. (p. 6256) developed a conditional knockout mouse in which talin1 was conditionally deleted in T cells. CD4+ T cell trafficking to peripheral lymph nodes was significantly reduced in mice lacking T cell expression of talin1. In addition, contact-dependent CD4+ T cell proliferation and cytokine production were significantly compromised in talin1-deficient CD4+ T cells. Further analysis revealed that talin1-deficient T cells formed weak interactions with APCs, but these transient contacts were sufficient to trigger TCR signaling. LFA-1 was able to polarize to contacts between talin1-deficient T cells and APCs similar to talin1-expressing control T cells. In contrast, the cytoskeletal molecules F-actin and vinculin were unable to polarize to these contacts in the absence of talin1, which prevented stable synapse formation and T cell arrest. Thus, talin1 appears to be a key molecule in sustaining T cell–APC interactions during synapse formation.

Dengue virus is an emerging mosquito-borne infection that can have dangerous consequences for humans if it results in dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). Defects in coagulation and fibrinolysis are among the manifestations of DHF/DSS. Chuang et al. (p. 6483) have characterized a mAb derived from a dengue virus-immunized mouse that crossreacts with a component of the fibrinolysis pathway. The authors observed that sera from dengue-infected humans or dengue virus-immunized mice were able to bind to plasminogen (Plg), a precursor molecule involved in fibrinolysis. The mAb 6H11 was derived from a dengue virus-immunized mouse and was specific to a dengue virus envelope protein. 6H11 crossreacted strongly with Plg and exhibited serine protease activity, which resulted in conversion of Plg to plasmin. 6H11-mediated Plg activation led to degradation of fibrin in platelet-poor plasma from mice or humans. In addition, i.v. injection of 6H11 into mice caused significantly higher levels of fibrinolysis compared with control mAb injection. These findings present a mechanism that may be responsible for the association of DHF/DSS with excessive fibrinolysis, and better inform selection of dengue virus vaccine candidate Ags in order to avoid potentially dangerous immune responses.

Summaries written by Christiana N. Fogg, Ph.D.