Effector CD4⁺ T cells recognize intravascular antigen presented by patrolling monocytes

Area of Science:

• Immunology
• Renal Physiology
• Cell Biology

Background:

• Effector CD4+ T cells typically respond to antigens outside blood vessels.
• The mechanisms of intravascular antigen recognition by CD4+ T cells remain unclear.
• Glomerular intrinsic cells do not express MHC class II (MHCII), suggesting other cells present antigens within glomeruli.

Purpose of the Study:

• To investigate how effector CD4+ T cells recognize intravascular antigens within the glomeruli.
• To identify the specific immune cells responsible for presenting intravascular antigens in the glomerular microvasculature.
• To elucidate the role of these antigen-presenting cells in initiating CD4+ T-cell-mediated glomerular inflammation.

Main Methods:

• Intravital multiphoton microscopy of mouse glomeruli.
• Observation of CD4+ T cell migration and interactions with MHCII-expressing cells.
• Assessment of T-cell activation markers (NFAT1 nuclear translocation) following intravascular antigen deposition.
• In vitro T-cell proliferation assays using monocytes.
• Monocyte depletion studies to evaluate their role in glomerular inflammation.

Main Results:

• CD4+ T cells migrate intravascularly within glomeruli and interact with patrolling MHCII-expressing immune cells.
• Intravascular antigen deposition in glomeruli induced CD4+ T-cell responses indicative of antigen recognition.
• MHCII-expressing monocytes were retained in glomerular capillaries and induced T-cell proliferation in vitro.
• Depletion of monocytes reduced CD4+ T-cell-dependent glomerular inflammation.

Conclusions:

• MHCII-expressing monocytes patrol glomerular capillaries and present intravascular antigens to CD4+ T cells.
• This interaction within glomerular capillaries initiates antigen-dependent inflammation.
• Monocytes play a critical role in initiating CD4+ T-cell-mediated glomerular inflammatory responses to intravascular antigens.