Severe deficiency in vaccine and immune responses to Streptococcus peumoniae of growth hormone (GH) deficient mice with GHRH gene ablation

Abstract

Event Abstract Back to Event Severe deficiency in vaccine and immune responses to Streptococcus peumoniae of growth hormone (GH) deficient mice with GHRH gene ablation Khalil Farhat1, 2, Gwennaëlle Bodart3, Anne-Simone Parent3, Roberto Salvatori4, Henri J. Martens2 and Vincent Geenen1* 1 Université de Liège, Belgium 2 GIGA Inflammation, Infection et Immunité, Université de Liège, Belgium 3 Centre Hospitalier Universitaire de Liège, Belgium 4 The Johns Hopkins Hospital, Johns Hopkins Medicine, United States The precise impact of the somatotrope axis upon the immune system is still highly debated. From neurons in the hypothalamic arcuate nucleus, growth hormone (GH) releasing hormone (GHRH) controls the entire GHRH/GH/IGF-1 somatotrope axis. We have previously shown that mice with generalized ablation of growth hormone (GH) releasing hormone (GHRH) gene (Ghrh-/-) have normal thymus and T-cell development, but present a marked spleen atrophy and relative B-cell lymphopenia. Therefore, in this study we have investigated vaccinal and anti-infectious responses of Ghrh-/- mice against Streptococcus (S) pneumoniae, a pathogen carrying T-independent antigens. Ghrh-/- mice were unable to trigger production of specific IgM after vaccination with either native pneumococcal polysaccharides (PPS, PPV23) or protein-PPS conjugate (PCV13). Human GH supplementation (Genotonorm 2µg/g for 5 weeks) of Ghrh-/- mice restored IgM response to PPV23 vaccine but not to PCV13 suggesting that GH could exert a specific impact on the spleen marginal zone that is strongly implicated in T-independent response against pneumococcal polysaccharides. After an intranasal administration of a sublethal dose of S. pneumoniae, wild type (WT) completely cleared bacteria after 24 h, as expected. In marked contrast, Ghrh-/- mice exhibited a dramatic susceptibility to S. pneumoniae infection with a time-dependent increase in lung bacterial load and a lethal bacteremia already after 24 h. Lungs of infected Ghrh-/- mice were massively infiltrated by inflammatory macrophages and neutrophils, while lung B cells were markedly decreased. The inflammatory transcripts signature was also significantly elevated in Ghrh-/- mice. By flow cytometry analysis, the percentage of spenic marginal and follicular B cells was signifantly decreased in the spleen of infected KO mice. The distribution of a special subset of splenic macrophages identified by an anti-macrophage receptor with collagenous structure (MARCO) was also also severely affected in the spleen of infected Ghrh-/- mice. To verify whether Ghrh-/- mice have a general susceptibility to pathogens, we infected WT and KO mice with a thymus-dependent antigen: the H1N1 murine influenza virus. Infected animals exhibit a restrained mobility from day 4 to day 10, associated with a rapid respiration and fever that reach the lowest level at day 10. No difference in body weight was observed between WT and KO mice after a sublethal dose of H1N1, and KO even gained more weight after 16 days. During a supralethal H1N1 infection, both strains reached death limit point at day 6 for Ghrh-/- mice or day 8 for WT mice. This animal model unambiguously demonstrates that the somatotrope GHRH/GH/IGF1 axis plays a vital and unsuspected role in vaccine and immunological defense against S. pneumoniae. In a translational perspective, the data indicate that spleen development and response to anti-pneumococcus vaccines could be cautiously monitored in children with isolated GH deficiency, from congenital and genetic origin in particular. Acknowledgements This study was supported by grants from Association of Specialization and Scientific Guidance (Lebanon), F.R.S-FNRS, Fonds Léon Fredericq, Wallonia and W-B Federation. VG is Research director at F.R.S-FNRS. We are grateful to L. Duwez, F. Olivier, G. Lambert and Pr P. Drion from the GIGA Animal Facility for animal management, as well as the Cell Imaging and Flow Cytometry GIGA Technological Platforms. We also thank Pfizer for kindly providing Genotonorm (recombinant hGH).