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Through immune memory, infections have a lasting effect on the host. While memory cells enable accelerated and enhanced responses upon re-challenge with the same pathogen, their impact on susceptibility to unrelated diseases is unclear. We identify a subset of memory T helper 1 (Th1) cells termed innate acting memory T (TIA) cells that originate from a viral infection and produce IFN-γ with innate kinetics upon heterologous challengein vivo. Activation of memory TIAcells is induced in response to IL-12 in combination with IL-18 or IL-33 but is TCR-independent. Rapid IFN-γ production by memory TIAcells is protective in subsequent heterologous challenge with the bacterial pathogenLegionella pneumophila. In contrast, antigen-independent re-activation of CD4+memory TIAcells accelerates disease onset in an autoimmune model of multiple sclerosis. Our findings demonstrate that memory Th1 cells can acquire additional TCR-independent functionality to mount rapid, innate-like responses that modulate susceptibility to heterologous challenges.

CD4

CD4+ T cells play a central role in orchestrating the immune response to a variety of pathogens but also regulate autoimmune responses, asthma, allergic responses, as well as tumor immunity. To cover this broad spectrum of responses, naive CD4+ T cells differentiate into one of several lineages of T helper cells, including Th1, Th2, Th17, and TFH, as defined by their cytokine pattern and function. The fate decision of T helper cell differentiation integrates signals delivered through the T cell receptor, cytokine receptors, and the pattern of co-stimulatory signals received. In this review, we summarize the contribution of co-stimulatory and co-inhibitory receptors to the differentiation and maintenance of T helper cell responses.

CD4+Foxp3+ Treg cells are essential for maintaining self-tolerance and preventing excessive immune responses. In the context of Th1 immune responses, co-expression of the Th1 transcription factor T-bet with Foxp3 is essential for Treg cells to control Th1 responses. T-bet-dependent expression of CXCR3 directs Treg cells to the site of inflammation. However, the suppressive mediators enabling effective control of Th1 responses at this site are unknown. In this study, we determined the signature of CXCR3+ Treg cells arising in Th1 settings and defined universal features of Treg cells in this context using multiple Th1-dominated infection models. Our analysis defined a set of Th1-specific co-inhibitory receptors and cytotoxic molecules that are specifically expressed in Treg cells during Th1 immune responses in mice and humans. Among these, we identified the novel co-inhibitory receptor CD85k as a functional predictor for Treg-mediated suppression specifically of Th1 responses, which could be explored therapeutically for selective immune suppression in autoimmunity.

SUMMARYThe impact of di-cationic pentamidine-analogues againstToxoplama gondii(Rh- and Me49-background) was investigated. The 72 h-growth assays showed that the arylimidamide DB750 inhibited the proliferation of tachyzoites ofT. gondii RhandT. gondii Me49with an IC50of 0·11 and 0·13μm, respectively. Pre-incubation of fibroblast monolayers with 1μmDB750 for 12 h and subsequent culture in the absence of the drug also resulted in a pronounced inhibiton of parasite proliferation. However, upon 5–6 days of drug exposure,T. gondiitachyzoites adapted to the compound and resumed proliferation up to a concentration of 1·2μm. Out of a set of 32 di-cationic compounds screened forin vitroactivity againstT. gondii,the arylimidamide DB745, exhibiting an IC50of 0·03μmand favourable selective toxicity was chosen for further studies. DB745 also inhibited the proliferation of DB750-adaptedT. gondii(IC50=0·07μm). In contrast to DB750, DB745 also had a profound negative impact on extracellular non-adaptedT. gondiitachyzoites, but not on DB750-adaptedT. gondii. Adaptation ofT. gondiito DB745 (up to a concentration of 0·46μm) was much more difficult to achieve and feasible only over a period of 110 days. In cultures infected with DB750-adaptedT. gondiiseemingly intact parasites could occasionally be detected by TEM. This illustrates the astonishing capacity ofT. gondiitachyzoites to adapt to environmental changes, at least underin vitroconditions, and suggests that DB745 could be an interesting drug candidate for further assessments in appropriatein vivomodels.

Coinhibitory receptors, such as CTLA-4 and PD-1, play a critical role in maintaining immune homeostasis by dampening T cell responses. Recently, they have gained attention as therapeutic targets in chronic disease settings where their dysregulated expression contributes to suppressed immune responses. The novel coinhibitory receptor TIGIT (T cell Ig and ITIM domain) has been shown to play an important role in modulating immune responses in the context of autoimmunity and cancer. However, the molecular mechanisms by which TIGIT modulates immune responses are still insufficiently understood. We have generated a panel of monoclonal anti-mouse TIGIT Abs that show functional properties in mice in vivo and can serve as important tools to study the underlying mechanisms of TIGIT function. We have identified agonistic as well as blocking anti-TIGIT Ab clones that are capable of modulating T cell responses in vivo. Administration of either agonist or blocking anti-TIGIT Abs modulated autoimmune disease severity whereas administration of blocking anti-TIGIT Abs synergized with anti–PD-1 Abs to affect partial or even complete tumor regression. The Abs presented in this study can thus serve as important tools for detailed analysis of TIGIT function in different disease settings and the knowledge gained will provide valuable insight for the development of novel therapeutic approaches targeting TIGIT.

Neospora caninum is an apicomplexan parasite that is capable of infecting, a wide range of tissues. The fact that Neospora represents an important abortion-causing parasite in cattle has transformed neosporosis research from an earlier, rather esoteric field, to a significant research topic, and considerable investments have been made in the last years to develop an efficacious vaccine or other means of intervention that would prevent infection and abortion due to N. caninum infection in cattle. Antigenic molecules associated with proteins involved in adhesion/invasion or other parasite-host-cell interaction processes can confer protection against Neospora caninum infection, and such proteins represent valuable targets for the development of a vaccine to limit economical losses due to neosporosis. Although not ideal, small laboratory animal models that mimic cerebral infection, acute disease and fetal loss upon infection during pregnancy have been used for the assessment of vaccine candidates, in parallel with studies on experimental infections in cattle. Herein, we review and critically assess these vaccination approaches and discuss potential options for improvements.

Neospora caninum is considered to be the main cause of bovine abortion in Europe and the USA, leading to considerable financial impact. Losses are caused directly by abortions or indirectly through breeding of calves with impaired viability. Due to the lack of effective chemotherapy against bovine neosporosis, there is a need to develop new anti-protozoal compounds, which would either eliminate the parasite or avoid its transmission. In order to identify compounds of interest, the in vitro activities of 41 di-cationic pentamidine derivatives were studied employing a transgenic N. caninum clone expressing beta-galactosidase as a reporter gene. The arylimidamide DB745, previously shown to be highly active against Leishmania donovani in vitro and in vivo, appeared as the most promising compound, with an IC50 of 80nM in 3-day growth assays and severely affecting both host cell invasion as well as intracellular proliferation. TEM of intracellular tachyzoites identified distinct alterations related to the nucleolus and the nuclear and cellular membrane. Long-term growth assays showed that DB745 acted parasiticidal upon the Nc-Liv isolate, but not against the Nc-1 isolate of N. caninum. In vivo studies in N. caninum (Nc-1 isolate) infected mice showed that daily intraperitoneal application of DB745 for a period of 14days resulted in a decreased number of clinically affected animals, and lower cerebral parasite burdens in DB745-treated mice compared to non-treated mice. These results illustrate the potential of dicationic arylimidamides for the treatment of N. caninum infections.

Im Sommer und Herbst 2011 wurden bei Milchkuhen aus dem Nordwesten der Niederlande und aus Nordrhein-Westfalen in Deutschland unspezifi sche Krankheitssymptome wie wassriger Durchfall, Fieber und Milchleistungsruckgang beobachtet, welche nach wenigen Wochen wieder abklangen. Bei den Abklarungen auf bekannte Viren konnte keine Krankheitsursache ermittelt werden. (Garigliany et al., 2012, Muskens et al., 2012). Beginnend im Dezember des folgenden Winters traten, uber ganz Deutschland und Holland verteilt, leichte bis schwerwiegende Missbildungen bei neuund totgeborenen Lammern und Kalbern auf. Die Muttertiere zeigten weder bei der Trachtigkeit noch bei der Geburt die oben beschriebenen Symptome. Unter den festgestellten Missbildungen waren Arthrogrypose, Torticollis, Skoliose, Kyphose, Brachygnathia inferior und eine unterschiedlich ausgepragte Hypoplasie des Grossund Kleinhirns und des Ruckenmarks haufi g (van den Brom et al., 2012). Im November 2011 wurde am Friedrich-Loffl er-Institut (FLI) in Deutschland eine Metagenom-Analyse der aus Plasmaproben isolierten DNA und RNA von im Oktober 2011 erkrankten Kuhen durchgefuhrt und ein fur Europa neuartiges Orthobunyavirus detektiert (Hoffmann et al., 2011). Der Erreger wurde nach der Herkunft der Proben Schmallenberg-Virus genannt. Das Virus wurde in der Folge auch in den missgebildeten Kalbern und Lammern nachgewiesen (Bilk et al., 2012). Beim neu entdeckten Virus handelt es sich um ein RNAVirus aus der Simbu-Serogruppe, welcher viele verschiedene sogenannte Arboviren (arthropod-borne viruses) angehoren. Phylogenetisch nahverwandte Viren («Shamonda-like»-Viren, z. B. Akabane), welche ebenfalls kongenitale Missbildungen und neurologische Veranderungen bei Rindern und kleinen Wiederkauern verursachen, sind in Afrika, Asien und Ozeanien schon seit Jahrzehnten bekannt (Al-Busaidy et al., 1987, Sellers et al., 1981). Die Ubertragung der Schmallenberg-Viren erfolgt durch den Stich von Gnitzen (Culicoides) und eventuell von Stechmucken sowie transplazentar (Rasmussen et al., 2012; van den Brom et al., 2012). Das Virus lasst sich nicht durch direkten Kontakt von Tier zu Tier zu ubertragen. Nach aktuellem Wissensstand sind Rinder, kleine Wiederkauer, aber auch Hirsche, Rehe, Alpakas und Muffl ons furs das Virus empfanglich (EFSA, 2012). Nach einer Infektion mit dem Schmallenberg-Virus konnen Rinder unspezifi sche Symptome wie Fieber, Durchfall, Appetitlosigkeit und einen massiven Milchleistungsruckgang bis auf die Halfte der Ausgangsleistung zeigen. Die sehr kurze Viramie dauert nur 1 bis 6 Tage, und die Symptome klingen innerhalb weniger Tage wieder ab. Bei adulten Ziegen und Schafen sind bisher nur in seltenen Fallen Symptome bekannt (Lievaart-Peterson et al., 2012). Ungefahr 10 Tage spater wurden Antikorper im Serum nachgewiesen (Hoffmann et al., 2012). Kommt es wahrend der Trachtigkeit von Rindern, Schafen und Ziegen zu einer Infektion des Muttertieres, so kann das Virus auf den Fotus ubertragen werden. Je nach Trachtigkeitsstadium kann die Infektion des Feten zu Abort, Fruhoder Totgeburt fuhren sowie schwerwiegende Missbildungen und Storungen des Zentralnervensystems verursachen. Diese Missbildungen werden als «Arthrogrypose-Hydranencephalie-Syndrom» (AHS) zusammengefasst und sind typisch fur Infektionen mit Viren aus der Simbu-Serogruppe. (OIE technical factsheet und Kurogi et al., 1977).

In order to achieve host cell entry, the apicomplexan parasite Neospora caninum relies on the contents of distinct organelles, named micronemes, rhoptries and dense granules, which are secreted at defined timepoints during and after host cell entry. It was shown previously that a vaccine composed of a mixture of three recombinant antigens, corresponding to the two microneme antigens NcMIC1 and NcMIC3 and the rhoptry protein NcROP2, prevented disease and limited cerebral infection and transplacental transmission in mice. In this study, we selected predicted immunogenic domains of each of these proteins and created four different chimeric antigens, with the respective domains incorporated into these chimers in different orders. Following vaccination, mice were challenged intraperitoneally with 2 × 10(6)N. caninum tachzyoites and were then carefully monitored for clinical symptoms during 4 weeks post-infection. Of the four chimeric antigens, only recNcMIC3-1-R provided complete protection against disease with 100% survivors, compared to 40-80% of survivors in the other groups. Serology did not show any clear differences in total IgG, IgG1 and IgG2a levels between the different treatment groups. Vaccination with all four chimeric variants generated an IL-4 biased cytokine expression, which then shifted to an IFN-γ-dominated response following experimental infection. Sera of recNcMIC3-1-R vaccinated mice reacted with each individual recombinant antigen, as well as with three distinct bands in Neospora extracts with similar Mr as NcMIC1, NcMIC3 and NcROP2, and exhibited distinct apical labeling in tachyzoites. These results suggest that recNcMIC3-1-R is an interesting chimeric vaccine candidate and should be followed up in subsequent studies in a fetal infection model.