Dr. Walker's research interests are broadly in the area of obligatory intracellular bacteria that are transmitted by arthropod vectors. Two research projects currently funded by the NIH are focused on immune mechanisms against rickettsiae and ehrlichiae and identification of the protein antigens that stimulate immunity. Although the diseases caused by rickettsiae include many long known and feared life threatening infections such as Rocky Mountain spotted fever and epidemic typhus, elucidation of their molecular composition and effector immune mechanisms remains productive lines of investigation. In contrast, human ehrlichioses are truly emerging infectious diseases that were unknown until recently and are causing increasingly prevalent, severe infections. Ehrlichial pathogenesis and immunity are in the process of being discovered and investigated at present for these novel organisms. His research on immunity pursues hypotheses involving studies of innate immunity including NKT cells, natural killer cells, and Î³Î´ T cells, and adaptive immunity including antibodies, endothelial biology, and T regulatory cells.
His investigative armamentarium includes outstanding mouse models of spotted fever and typhus rickettsioses and monocytotropic ehrlichioses, which lend themselves to the study of pathogenesis as well as immunity. The molecular studies of rickettsiae are focused on rickettsial virulence mechanisms, while the investigations of Ehrlichia chaffeensis, E. canis, E. muris, and Ixodes ovatus Ehrlichia are focused on immunodominant proteins as vaccine candidates. Other projects include development of vaccines against R. prowazekii, E. canis, and E. chaffeensis, development of new diagnostic tests utilizing patented intellectual property sponsored by the Clayton Foundation, and international collaborations in Mexico, Brazil, Cameroon, and Portugal with opportunities for field and laboratory work in tropical locations.
His research is greatly enhanced by collaborative efforts involving the molecular expertise of Drs. Xuejie Yu, Jere McBride, and Donald Bouyer, the immunologic knowledge and skills of Drs. Gustavo Valbuena and Lynn Soong, the ultrastructural expertise of Dr. Vsevolod Popov, and the cell biology skills of Dr. Juan Olano including confocal microscopy. New initiatives include vector biology of tick-borne ehrlichial and rickettsial infections.