Background: The severe acute respiratory syndrome (SARS) outbreak in 2003 affected 29 countries. The SARS outbreak was unique in its rapid transmission and it resulted in heavy stress in first-line healthcare workers, particularly in the emergency department. Aim : To determine the influence of SARS on the psychological status, including post-traumatic stress disorder (PTSD) symptoms, of the staff in the emergency department. Methods: To investigate whether different working conditions in the hospital led to different psychological effects on healthcare workers, the psychological effect on emergency department staff in the high-risk ward was compared with that on psychiatric ward staff in the medium-risk ward. Davidson Trauma Scale-Chinese version (DTS-C) and Chinese Health Questionnaire-12 (CHQ-12) items were designed to check the psychological status of the staff in the month after the end of the SARS outbreak. Results: 86 of 92 (93.5%) medical staff considered the SARS outbreak to be a traumatic experience. The DTS-C scores of staff in the emergency department and in the psychiatric ward were significantly different (p = 0.04). No significant difference in CHQ score was observed between the two groups. Emergency department staff had more severe PTSD symptoms than staff in the psychiatric ward. Conclusion: SARS was a traumatic experience for healthcare providers in Taiwan. Most staff in the emergency department and in the psychiatric ward had PTSD. Emergency department staff had more severe PTSD symptoms than staff in the psychiatric ward.

T cell activation, a critical event in adaptive immune responses, follows productive interactions between T cell receptors (TCRs) and antigens, in the form of peptide-bound major histocompatibility complexes (pMHCs) on the surfaces of antigen-presenting-cells. Upon activation, T cells can lyse infected cells, secrete cytokines, such as interferon-γ (IFN-γ), and perform other effector functions with various efficiencies that directly depend on the binding parameters of the TCR-pMHC complex. The mechanism that relates binding parameters to the efficiency of activation of the T cell remains controversial; some studies suggest that the dissociation constant (K D ) determines the response (the "affinity model"), whereas others suggest that the off-rate (k off ) is critical (the "productive hit rate model"). Here, we used mathematical modeling to show that antigen potency, as determined by the EC 50 , the functional correlate that is used to support K D -based models, could not be used to discriminate between the affinity and productive hit rate models. Our theoretical work showed that both models predicted a correlation between antigen potency and K D , but only the productive hit rate model predicted a correlation between maximal efficacy (E max ) and k off . We confirmed the predictions made by the productive hit rate model in experiments with cytotoxic T cell clones and a panel of pMHC variants. Therefore, we suggest that the activity of an antigen is determined by both its potency and maximal efficacy. We discuss the implications of our findings to the practical evaluation of T cell activation, for example in adoptive immunotherapies, and relate our work to the pharmacological theory of dose-response. † To whom correspondence should be addressed. omer.dushek@path.ox.ac.uk (O.D.); anton.vandermerwe@path.ox.ac.uk (P.A.V.D.M.) . ‡ Present address: Immunocore Limited, Abingdon, OX14 4RX, UK.

High levels of circulating virus-specific CD4(+) T cells to two viral internal proteins (nucleoprotein and matrix) in the first phase of infection are associated with subsequent development of severe IAV infection. This finding could be an early and specific marker for ensuing clinical deterioration. Contrasting levels of antigen-specific CD8(+) T cells in lungs and blood have implications on design and analysis of clinical trials for T-cell vaccines because measurements of T cells in the periphery may not reflect events in the lungs.