Different response requirements for IFNgamma production in ELISPOT assays by CD4+ T cells from mice early and late after immunization

Plant-expressed HA as a seasonal influenza vaccine candidate

Influenza is a globally important respiratory pathogen that causes a high degree of morbidity and mortality annually. Although current vaccines are effective against virus infection, new strategies need to be developed to satisfy the global demand for an influenza vaccine. To address this point, we have engineered and produced the full-length hemagglutinin (HA) protein from the A/Wyoming/03/03 (H3N2) strain of influenza in plants. The antigenicity of this plant-produced HA was confirmed by ELISA and single-radial immunodiffusion (SRID) assays. Immunization of mice with plant-produced HA resulted in HA-specific humoral (IgG1, IgG2a and IgG2b) and cellular (IFNgamma and IL-5) immune responses. In addition, significant serum hemagglutination inhibition (HI) and virus neutralizing (VN) antibody titers were obtained with an antigen dose as low as 5mug. These results demonstrate that plant-produced HA protein is antigenic and can induce immune responses in mice that correlate with protection.

Transient inhibition of Th1-type cytokine production by CD4 T cells in hepatitis B core antigen immunized mice is mediated by regulatory T cells

The non-cytopathic hepatitis B virus (HBV) can induce chronic infections characterized by weak and limited T cell responses against the virus. The factors contributing to the failure to clear HBV and subsequent development of chronic HBV infections are not clearly understood, but a strong interferon-gamma (IFN-gamma) response by CD4+ T cells against the nucleocapsid hepatitis B core antigen (HBcAg) of the virus appears to be important for viral clearance. The present study documents depressed numbers of CD4+ T cells secreting IFN-gamma and interleukin-2 (IL-2) in enzyme-linked immunospot assay (ELISPOT) assays restimulated for 24 hr with antigen following both primary and secondary immunizations of mice with recombinant hepatitis B core antigen (rHBcAg). The kinetics of these responses showed that the depression occurred following a peak response and lasted approximately 2 weeks before returning to the previous peak levels. The depression was abrogated by depletion of CD25+ cells prior to culture in the ELISPOT assay, suggesting inhibition by regulatory T cells. This inhibition of IFN-gamma and IL-2 production was also reversed by in vitro restimulation of the test cells for 48 hr rather than 24 hr in the assay. No such transient, reversible inhibition was detected in the production of IL-5, a Th2-type cytokine. The inhibition in cytokine production did not appear to correlate with the number of antibody-secreting cells or the isotypes produced. This delay by regulatory T cells of Th1-type cytokine production could contribute to viral persistence in chronic HBV infection by interfering with the critical role IFN-gamma plays in protection against viral infections.