CD200 Receptor Controls Sex-Specific TLR7 Responses to Viral Infection

Immunological checkpoints, such as the inhibitory CD200 receptor (CD200R), play a dual role in balancing the immune system during microbial infection. On the one hand these inhibitory signals prevent excessive immune mediated pathology but on the other hand they may impair clearance of the pathogen. We studied the influence of the inhibitory CD200-CD200R axis on clearance and pathology in two different virus infection models. We find that lack of CD200R signaling strongly enhances type I interferon (IFN) production and viral clearance and improves the outcome of mouse hepatitis corona virus (MHV) infection, particularly in female mice. MHV clearance is known to be dependent on Toll like receptor 7 (TLR7)-mediated type I IFN production and sex differences in TLR7 responses previously have been reported for humans. We therefore hypothesize that CD200R ligation suppresses TLR7 responses and that release of this inhibition enlarges sex differences in TLR7 signaling. This hypothesis is supported by our findings that in vivo administration of synthetic TLR7 ligand leads to enhanced type I IFN production, particularly in female Cd200−/− mice and that CD200R ligation inhibits TLR7 signaling in vitro. In influenza A virus infection we show that viral clearance is determined by sex but not by CD200R signaling. However, absence of CD200R in influenza A virus infection results in enhanced lung neutrophil influx and pathology in females. Thus, CD200-CD200R and sex are host factors that together determine the outcome of viral infection. Our data predict a sex bias in both beneficial and pathological immune responses to virus infection upon therapeutic targeting of CD200-CD200R

Lack of CD200 Enhances Pathological T Cell Responses during Influenza Infection

Influenza virus infection can be accompanied by life-threatening immune pathology most likely due to excessive antiviral responses. Inhibitory immune receptors may restrain such overactive immune responses. To study the role of the inhibitory immune receptor CD200R and its ligand CD200 during influenza infection, we challenged wild-type and CD200(-/-) mice with influenza virus. We found that CD200(-/-) mice in comparison to wild-type controls when inoculated with influenza virus developed more severe disease, associated with increased lung infiltration and lung endothelium damage. CD200(-/-) mice did develop adequate adaptive immune responses and were able to control viral load, suggesting that the severe disease was caused by a lack of control of the immune response. Interestingly, development of disease was completely prevented by depletion of T cells before infection, despite dramatically increased viral load, indicating that T cells are essential for the development of disease symptoms. Our data show that lack of CD200-CD200R signaling increases immune pathology during influenza infection, which can be reduced by T cell depletion. The Journal of Immunology, 2009, 183: 1990-1996

Immune checkpoints and rheumatic diseases : what can cancer immunotherapy teach us?

The recent success of immune checkpoint blockade in cancer therapy illustrates the importance of the inhibitory receptors cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) and programmed cell death protein 1 (PD1) in the regulation of antitumour immune responses. However, blocking signalling by these inhibitory immune checkpoint receptors is also associated with substantial inflammatory effects that can resemble autoimmune responses, which is consistent with the role of these receptors in protecting the host from excessive inflammation. The human genome encodes over 300 inhibitory receptors, which represent as many opportunities to modulate inflammation in a disease-specific and tissue-specific manner. We argue that rheumatologists and oncologists should join forces to study these inhibitory immune molecules. An improved understanding of these immune checkpoints will enable both fields to make progress in exploiting inhibitory immune receptors therapeutically. In this Review, we discuss data from studies reporting the adverse inflammatory effects of cancer therapies that target immune checkpoints. We discuss the potential implications of these findings on the biological understanding of autoimmune rheumatic diseases and highlight therapeutic strategies that could be used to target inhibitory receptors for the treatment of these conditions