Ovalbumin injected with complete Freund's adjuvant stimulates cytolytic responses

Abstract

CD8+ cytotoxic T lymphocytes (CTL) recognize antigens (Ag) associated with class I major histocompatibility complex (MHC) molecules. Endogenously synthesized protein Ag are processed into peptides in the cytoplasm and transported to the endoplasmic reticulum where they are bound by class I proteins. Exogenous Ag do not enter the class I processing pathway of most cells and thus do not activate CD8+ CTL. Nevertheless, several investigators have reported that immunization with exogenous Ag can activate CD8+ T cells that have immunoregulatory activity. To determine how exogenous Ag entered the class I pathway in vivo and whether immunosuppressive CD8+ T cells were cytolytic, we have shown in this report that injection with OVA emulsified in the complete Freund's adjuvant (CFA) primed CD8+, class I MHC-restricted, OVA-specific CTL in mice. These CTL recognize the OVA257-264 epitope, produce tumor necrosis factor-alpha and interferon-gamma upon activation. Both oil and mycobacteria components in CFA were required for inducing CTL responses. Priming was not attributed to direct sensitization of class I-bearing cells by contaminating peptides. Rather, phagocytic cells, but not CD4+ helper T cells, were required for priming CD8+ CTL by OVA-CFA. Thus, OVA in CFA is taken up by antigen-presenting cells and processed into the class I pathway by phagocytic cells in vivo. In addition, CTL induced by OVA-CFA suppressed the antibody response to OVA in adoptive recipients. These results suggest that CD8+ CTL specific for exogenous proteins might be routinely stimulated by injecting proteins in conventional adjuvants and that such cells have the potential to regulate immune responses in vivo.

A Soluble Lymphocyte Activation Gene-3 Molecule Used as a Vaccine Adjuvant Elicits Greater Humoral and Cellular Immune Responses to Both Particulate and Soluble Antigens

“…Nonetheless, some protein Ags, such as OVA emulsified in CFA (15) or adsorbed onto alum (the present study), may elicit CD8 ϩ MHC class I-restricted CTLs. Innovative adjuvant formulations, such as immune-stimulating complexes (16), liposomes (17,18), or saponins (19 -21), that facilitate in vivo priming of CD8 ϩ CTLs by protein Ags are now being developed.…”

Injection of Soluble Antigen into the Anterior Chamber of the Eye Induces Expansion and Functional Unresponsiveness of Antigen-Specific CD8+ T Cells

“…The injection of OVA in CFA primes for CTL responses that are mediated by CD8 ϩ ␣␤ T cells specific for OVA 257-264 presented by H-2K b (12). However, the frequency of these Ag-specific T cells in naive, as well as immunized, mice is below the threshold of detection by flow cytometry (data not shown).…”

“…However, phagocytic cells have been shown to process exogenous proteins, load peptides onto MHC class I molecules, and stimulate CD8 ϩ T cells (11). Moreover, mice given OVA emulsified in CFA display robust Ag-specific CTL responses (12,13). Induction of this CTL response requires adjuvant and phagocytic cells (13).…”

“…However, CTL responses induced by OVA in CFA are independent of CD4 ϩ T cells (12). Other potential mechanisms that could account for the inhibition of CTL activity include clonal deletion, functional unresponsiveness, immune deviation of CD8 ϩ T cells, or activation of regulatory cells.…”

pH-Sensitive fusogenic polymer-modified liposomes as a carrier of antigenic proteins for activation of cellular immunity

“…To evaluate the potential of MGluPG liposomes as an adjuvant, we compared their induced CTLs activity with that of CFA, which is widely used for induction of immune responses [26]. The result is also presented in Fig.…”