Effective CD4 T cell priming requires repertoire scanning by CD301b⁺ migratory cDC2 cells upon lymph node entry

Area of Science:

• Immunology
• Cellular Biology
• Adaptive Immunity

Background:

• Initiating adaptive immunity requires scanning millions of lymphocytes to identify rare antigen-specific clones.
• While CD4 T cell activation is well-studied, the cellular mechanisms for cognate clone selection remain unclear.

Purpose of the Study:

• To elucidate the cellular mechanisms governing the selection of cognate CD4 T cell clones within lymph nodes.

Main Methods:

• Investigated the behavior of recently homed naïve polyclonal CD4 T cells in lymph nodes.
• Characterized the role of CD301b+ dendritic cells (DCs) in retaining and priming CD4 T cells.

Main Results:

• Naïve CD4 T cells exhibit stop-and-go traffic, temporarily retained in lymph nodes.
• CD301b+ DCs, a subset of migratory cDC2 cells, are found near high endothelial venules.
• These DCs retain CD4 T cells via MHCII-dependent, antigen-independent mechanisms, providing priming stimuli.

Conclusions:

• The stop-and-go trafficking of CD4 T cells creates a crucial time window for antigen scanning and priming.
• CD301b+ DCs act as an "immunological display window," enhancing the efficiency of cognate CD4 T cell clone selection.