Macrophages, dendritic cells or B lymphocytes have been shownto play a major role in the presentation of soluble antigensto CD4
+ T cells. In contrast, the capacity of these cells topresent particulate antigens such as bacterial or parasiticantigens to T cells remains controversial. To investigate thisquestion, well defined particulate antigens were prepared bycovalent linkage of proteins or peptides to 1 µm in diametersynthetic microspheres. The T cell immunogenicity of such particulateantigens was analyzed
in vitro and
in vivo.
In vitro, a solubleprotein such as hen egg lysozyme (HEL) coupled to beads stimulateda strong proliferative T cell response of lymph node cells fromHEL-primed mice or of specific T cell hybridomas. HEL coupledto beads was presented to the specific T cell hybridomas bysplenocytes or by peritoneal macrophages, but not by lymphomaB cells. Immunization of mice with several different proteinantigens or with a synthetic peptide covalently linked to beadsinduced strong CD4
+ T cell responses in the absence of adjuvant.The strong
in vivo immunogenicity of proteins coupled to beadsdid not result from a non-specific adjuvant effect of beadssince covalent linkage of the antigen to beads was strictlyrequired to induce T cell responses in the absence of adjuvant.
In vivo treatment by carrageenan showed that macrophages arerequired for the
in vivo stimulation of T cell responses bythese particulate antigens. Thus, these results demonstratedthe role of phagocytic cells, especially macrophages, for
invivo presentation of particulate antigens. These particulateantigens represent an interesting approach for the developmentof new vaccines, and for the
in vivo analysis of the role ofvarious antigen presenting cells in T cell activation and differentiation.
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