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?(Fig.4,4, ideal panel). to be a limiting element for VLP-based T-cell vaccines. Cytotoxic T cells (CTL) are key lymphocytes for the clearance of many viral and bacterial infections and for the eradication of tumors. The goal of most restorative vaccination strategies is definitely, consequently, the induction of specific CTLs. However, in the absence of intracellular replication, it is usually hard to induce efficient CTL reactions (2, 7, 37). An important reason for this inefficiency is the difficulty for an exogenous antigen to reach the major histocompatibility complex (MHC) class I pathway. In general, exogenous antigens reach the MHC class II pathway while only endogenous antigens efficiently gas the MHC class I pathway (7, 13). Accordingly, immunization with inactivated viral particles usually fails to induce CTL reactions (3, 18). This makes it thorny to generate powerful vaccines based on recombinant proteins. Virus-like particles (VLPs) are an interesting exception, since they are able to efficiently reach the MHC class I pathway (4, 14, 24, 27, 29) in the absence DAPK Substrate Peptide of illness or intracellular replication. Therefore, VLPs are consequently promising restorative vaccine candidates that may induce efficient T-cell reactions in the absence of viral replication. It is generally assumed that vaccine-specific antibodies impair the induction of protecting immune reactions upon vaccination. A basis for this assumption may be that many vaccines are based on attenuated, but replication proficient, viral strains (1, 22). Under these conditions, the attenuated computer virus may be neutralized from the antibodies, resulting in reduced replication and antigen DAPK Substrate Peptide weight. As a consequence, T-cell induction is definitely impaired. The situation for nonreplicating vaccines is definitely less obvious, and reports of reduced T-cell reactions in the presence of specific antibodies are rare (8, 30). In fact, it may be expected that antibodies enhance opsonization of the vaccine, leading to improved antigen demonstration. Thus, it seems possible that the presence of specific antibodies may facilitate CTL activation. In support of this, tumor-specific T-cell reactions were reported to be enhanced rather than reduced by the presence of specific antibodies (9, 15). Moreover, immune complexes efficiently reach the MHC class I pathway upon binding to Fc receptors, which facilitates induction of CTL reactions (25). To analyze the part of specific antibodies in regulating VLP-induced T-cell reactions, we used VLPs based on the hepatitis B computer virus DAPK Substrate Peptide core antigen (HBcAg) fused to lymphocytic choriomeningitis computer virus (LCMV)-derived MHC class I-restricted peptide p33 (23) or MHC class II-restricted peptide p13 (20). p33-VLPs have been previously shown to be efficiently cross-presented by dendritic cells and macrophages partly by a transporter associated with antigen control (Faucet)-independent mechanism (27). In this study, we assessed the influence of specific antibodies within the demonstration of peptides p33 (MHC class I) and p13 (MHC class II) in vitro and in vivo and on the induction of specific T-cell reactions. We observed that antigen demonstration was not affected in vitro or in vivo by the presence of specific antibodies. Moreover, protecting immunity could be founded in carrier vaccinated animals. Therefore, carrier suppression by VLP-specific antibodies Rabbit polyclonal to AHCYL1 was of small importance for VLP-based vaccination. MATERIALS AND METHODS Viruses and virus-like particles. LCMV isolate WE was originally from R. M. Zinkernagel (Institute of Experimental Immunology, University or college Hospital, Zrich, Switzerland) and propagated on L929 cells (6). Computer virus titers were determined by a focus-forming assay on MC57 fibroblasts. The generation, production, and purification of p33-VLPs have been described earlier (33). p13-VLPs, to which the LCMV-derived p13 epitope (sequence GLNGPDIYKGVYQFKSVEFD) was genetically fused via a 6-amino-acid linker (RSSGMY) to the C terminus of the HBcAg. Production and purification of p13-VLPs was performed as explained previously (32). Mice and carrier immunization. Woman C57BL/6 mice aged between 8 and 12 weeks were purchased from Harlan Netherlands B.V. (Horst, The Netherlands). Transgenic mice expressing a T-cell receptor (TCR).