Host Genetic Determinants of Vaccine-Induced Eosinophilia During Respiratory Syncytial Virus Infection 1 Tracy Hussell, 2 Andrew Georgiou, Tim E. Sparer, Stephen Matthews, Pietro Pala, and Peter J. M. Openshaw In BALB/c mice, sensitization with the attachment protein (G) of respiratory syncytial virus (RSV) leads to CD4 1 T cell-mediated lung eosinophilia during subsequent challenge with RSV. To determine the host genetic influences on this model of lung eosino- philia, we tested 15 different inbred mouse strains. Eosinophilia developed in all H-2 d (BALB/c, DBA/2n, and B10.D2), but not in H-2 k (CBA/Ca, CBA/J, C3H, BALB.K, or B10.BR) mouse strains. Among H-2 b mice, 129 and BALB.B developed eosinophilia, whereas C57BL/6 and C57BL/10 did not. Testing first generation crosses between sensitive and resistant strains showed that eosinophilia developed in all H-2 dxk (n 5 5), irrespective of background genes, but not in H-2 dxb (n 5 2) mice. In vivo depletion of CD8 1 T cells or IFN-g rendered C57BL/6, but not BALB.K mice, susceptible to eosinophilia. Analysis of B10 recombinant mice showed that the D d allele (in B10.A(5R) mice) prevented CD8 1 T cell accumulation in the lung, resulting in intense lung eosin- ophilia. However, the D b allele (in B10.A(2R) and B10.A(4R) mice) supported CD8 1 T cell expansion and prevented eosinophilia. Intracellular cytokine staining showed that lung eosinophilia correlated with reduced IFN-g and increased IL-10 expression in lung T cells. These results are compatible with the unifying model that Th2 cells mediate the disease but can be inhibited by CD8 1 T cells secreting IFN-g. Our findings have important implications for the development of protective, nonpathogenic vaccines for RSV disease. The Journal of Immunology, 1998, 161: 6215– 6222. A lthough more than forty years have elapsed since the discovery of respiratory syncytial virus (RSV), 3 the dis- ease that it causes remains an important global problem. Bronchiolitis is the most common single cause of hospitalization during infancy in the western world, most cases of which are caused by RSV. Reinfections occur throughout life and may cause severe problems in the elderly and immunocompromised individ- uals. In the 1960s, vaccine trials using formalin inactivated virus proved disastrous, causing exacerbated lung disease and, in some cases, death among vaccine recipients. Although the World Heath Organization, many governmental bodies, and industrial organiza- tions have identified RSV as a major target for vaccine develop- ment, a safe and effective vaccine has yet to be developed for human use. The BALB/c mouse model of RSV infection reproduces some important features of the human disease and has provided many insights into possible protective and pathogenic immune processes in man. Protective Ab responses are directed primarily against the fusion (F) and attachment (G) glycoproteins, both of which are expressed on the surface of the virion. Vaccination with F ex- pressed by recombinant vaccinia virus (rVV) generates Ab, cyto- toxic T cells, and CD4 1 Th1 cells after virus challenge (1– 4), whereas the glycoprotein G of RSV (rVV-G) leads to Ab produc- tion and CD4 1 Th2 cells, but no detectable cytotoxic T cells (5–9). The patterns of lung pathology after virus challenge are also dis- tinctive, in that F-primed mice develop augmented lung disease characterized by lung hemorrhage and neutrophilia, whereas G- primed mice develop pulmonary eosinophilia (10, 11). Pulmonary eosinophilia was also found in the lungs and periph- eral blood of some children vaccinated with formalin inactivated RSV (see, for example, Ref. 12). To improve our understanding of vaccine augmentation, we and others have performed extensive studies of the immune determinants of RSV-induced lung eosin- ophilia in BALB/c mice sensitized to G. In drawing general con- clusions about the relevance of this response to disease in diverse hosts, mapping genetic responses in inbred mice appears vital. It is well established that CD4 1 T cells are instrumental in causing eosinophilic disease augmentation, and that CD8 1 T cells making IFN-g may be crucial regulators of this response (5, 13). MHC gene effects are therefore likely to play a critical role in the genetic control of augmented RSV disease. Associations between MHC and susceptibility to infection have been reported (14 –18) and indicate the difficulties encountered when trying to design vaccines for outbred human populations. Different inbred strains of mice have provided an insight into the influence of MHC haplotype on the outcome of infection in many infectious disease models. How- ever, there has been no systematic study of the genetic influences on the induction of vaccine-augmented pathology during RSV infection. In the present studies, we sought to determine the immunologic mechanisms and genetic influences on RSV-induced lung eosino- philia using 15 inbred and 7 first generation (F 1 ) crossbred mice. Our results indicate that eosinophilic lung disease requires CD4 1 T cell recognition, and that, in mouse strains susceptible to eosin- ophilia, CD8 1 T cells secreting IFN-g play an important regula- tory role. The results obtained using different inbred and recom- binant mouse strains may explain the variability in the response to Respiratory Medicine, National Heart and Lung Institute, Imperial College of Sci- ence, Technology and Medicine, London, United Kingdom Received for publication May 13, 1998. Accepted for publication July 31, 1998. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This work was supported by The Wellcome Trust, U.K. 2 Address correspondence and reprint requests to Dr. Tracy Hussell, Respiratory Med- icine, National Heart and Lung Institute, Imperial College of Science, Technology and Medicine, St Mary’s Hospital, Norfolk Place, London W2 1PG, U.K. E-mail address: t.hussell@ic.ac.uk 3 Abbreviations used in this paper: RSV, respiratory syncytial virus; F, fusion gly- coprotein; G, attachment protein; rVV, recombinant vaccinia virus; b-gal, b-galac- tosidase; BAL, bronchoalveolar lavage. Copyright © 1998 by The American Association of Immunologists 0022-1767/98/$02.00