Analysis of the cells involved in the lymphoproliferative response to Coxiella burnetii antigens
Vaccination with an inactivated, whole cell, Q fever vaccine (Q‐vax) induces lasting antibody conversion and a positive delayed‐type hypersensitivity (DTH) skin reaction in about 60% of recipients but a long‐lasting positive lymphoproliferative or mitogenic response to C. burnetii antigens with peripheral blood mononuclear cells (PBMC) in 85–95% of subjects. Analysis of the lymphoproliferative response to C. burnetii antigens has now been made by fractionationreconstitution experiments with PBMC from vaccinees, from past infections, and from healthy controls. The major contributor to the response in immune subjects proved to be the T lymphocyte. T cells were stimulated by both the phase I and phase II antigens of two prototype strains of C. burnetii and responses were greatly amplified by addition of IL‐2. Similar T lymphocyte stimulation profiles were obtained with the ‘Priscilla’ strain of C. burnetii which represents a different biotype of Coxiella isolated from Q fever endocarditis; Q‐vax is therefore likely to protect against endocarditis strains. Fractionation‐reconstitution experiments with T and B cells from vaccinees and subjects infected in the past, using various antigenic or haptenic fractions from C. hurnetii indicate that protein, non‐lipopolysaccharide components of the organism are responsible for the mitogenic response of immune T cells. However, the role of the lipopolysaccharide in the protective immunogen has still to be defined.