Mutations in human CD4 impair the functional interaction with different human and mouse class II isotypes and alleles

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• The CD4 molecule acts as a co-receptor, crucial for T cell activation by binding to class II Major Histocompatibility Complex (MHC) molecules.
• Understanding the structural basis of CD4-class II MHC interactions is vital for dissecting immune responses and developing targeted therapies.

Purpose of the Study:

• To investigate the structure-function relationship of the CD4-class II MHC interaction.
• To assess the efficiency of interspecies CD4/class II interactions using human CD4 (h-CD4) and murine CD4 (m-CD4).

Main Methods:

• Utilized two functional assays with a murine T cell hybridoma expressing h-CD4 or m-CD4.
• Assessed T cell responses against antigen-presenting cells (APCs) co-expressing H-2Dd with various human and murine class II alleles.
• Conducted co-receptor assays using bacterial superantigen staphylococcal enterotoxin B to evaluate CD4 enhancement of T cell responses.

Main Results:

• Both h-CD4 and m-CD4 significantly enhanced T cell responses to H-2Dd, confirming efficient interspecies CD4/class II interactions.
• Mutations and deletions in h-CD4 affected interactions with both human and murine class II molecules, indicating conserved structural features.
• h-CD4 and m-CD4 enhanced T cell responses to staphylococcal enterotoxin B, further supporting conserved CD4-class II MHC interaction mechanisms.

Conclusions:

• The CD4-class II MHC interaction is functionally conserved across species.
• Specific structural elements of CD4 are critical for its interaction with both human and murine class II MHC molecules.
• These findings provide insights into the molecular mechanisms underlying T cell recognition and immune regulation.