In vivo activation of naive CD4⁺ T cells in nasal mucosa-associated lymphoid tissue following intranasal immunization with recombinant Streptococcus gordonii

The antigen-specific primary activation of CD4⁺ T cells was studied in vivo by adoptive transfer of ovalbumin-specific transgenic T cells (KJ1-26⁺ CD4⁺) following intranasal immunization with recombinant Streptococcus gordonii. A strain of S. gordonii expressing on its surface a model vaccine antigen fused to the ovalbumin (OVA) peptide from position 323 to 339 was constructed and used to study the OVA-specific T-cell activation in nasal mucosa-associated lymphoid tissue (NALT), lymph nodes, and spleens of mice immunized by the intranasal route. The recombinant strain, but not the wild type, activated the OVA-specific CD4⁺ T-cell population in the NALT (89% of KJ1-26⁺ CD4⁺ T cells) just 3 days following immunization. In the cervical lymph nodes and in the spleen, the percentage of proliferating cells was initially low, but it reached the peak of activation at day 5 (90%). This antigen-specific clonal expansion of KJ1-26 ⁺ CD4⁺ T cells after intranasal immunization was obtained with live and inactivated recombinant bacteria, and it indicates that the NALT is the site of antigen-specific T-cell priming.