Immunopathology of Bartonella vinsonii (berkhoffii) in experimentally infected dogs

Following natural infection with Bartonella, dogs and humans develop compar able disease manifestations including endocarditis, peliosis hepatis, and g ranulomatous disease. As the immunologic response to infection in these hos ts has not been clearly established, data presented here was derived from t he experimental infection of six specific pathogen free (SPF) beagles with a known pathogenic strain of Bartonella. Six dogs were inoculated intraveno usly with 10(9) cfu of B. vinsonii ssp. berkhoffii and six control dogs wer e injected intravenously with an equivalent volume of sterile saline. Despi te production of substantial levels of specific antibody, blood culture and molecular analyses indicated that Bartonella established chronic infection in these dogs. Flow cytometric analysis of monocytes indicated impaired ba cterial phagocytosis during chronic Bartonella infection. There was also a sustained decrease in the percentage of CD8+ lymphocytes in the peripheral blood. Moreover, modulation of adhesion molecule expression (down-regulatio n Of L-selectin, VLA-4, and LFA-1) on CD8+ lymphocytes suggested quantitati ve and qualitative impairment of this cell subset in Barton ella-infected d ogs. When compared with control dogs, flow cytometric analysis of lymph nod e (LN) cells from B, vinsonii infected dogs revealed an expanded population of CD4+ T cells with an apparent naive phenotype (CD45RA + /CD62L + /CD49D (dim)). However, fewer B cells from infected dogs expressed cell-surface MH C H, implicating impaired antigen presentation to helper T cells within LN. Taken together, results from this study indi-cate that B. vinsonii establi shes chronic infection in dogs which may result in immune suppression chara cterized by defects in monocytic phagocytosis, an impaired subset of CD8+ T lymphocytes, and impaired antigen presentation within LN. (C) 2001 Elsevie r Science B.V. All rights reserved.