The development of CD4+ T effector cells during the type 2 immune response

Area of Science:

• Immunology
• Cellular Immunology
• T cell differentiation

Background:

• The development of T helper (Th) cells and immune responses, specifically type 1 (IFN-gamma producing) and type 2 (IL-4 producing), is complex and influenced by multiple signaling pathways.
• Signal strength delivered to T cells and innate immune responses initiated by antigen-presenting cells (APCs) play critical roles in determining the balance between type 1 and type 2 immune responses.
• T cell receptor (TCR), CD4, and costimulatory molecule interactions contribute to signal strength, with type 2 responses showing particular dependence on coreceptor and costimulatory molecule availability.

Purpose of the Study:

• To investigate the role of costimulatory molecules, specifically B7 ligands and CD28, in the development and maintenance of the type 2 immune response.
• To elucidate the contribution of signal strength and innate immune stimuli in directing T helper cell differentiation towards a type 2 phenotype.
• To understand the specific roles of CD28 and CTLA-4 in the context of type 2 immune responses, particularly in response to infectious pathogens.

Main Methods:

• Studies involving B7-2-deficient mice to assess the impact of B7-2 deficiency on type 2 immune responses.
• Analysis of CD28 knockout (CD28-/-) mice to evaluate the necessity of CD28 for IL-4 producing T cell development.
• Examination of T cell receptor (TCR), CD4, and costimulatory molecule interactions in modulating T cell signaling strength.

Main Results:

• B7 ligand interactions, specifically CD28 binding to B7-1 or B7-2, are essential for initiating the type 2 immune response.
• While B7-2-deficient mice exhibit an intact initial type 2 response, its sustenance is impaired, highlighting B7-2's importance in later stages.
• Type 2 responses to pathogens are pronounced in CD28-/- mice, suggesting that alternative costimulatory pathways can compensate for CD28's absence in IL-4 producing T cell development.

Conclusions:

• Costimulatory molecule interactions are critical regulators of T helper cell differentiation and the subsequent type 2 immune response.
• B7-2 plays a significant role in sustaining type 2 immune responses beyond the initial activation phase.
• The development of IL-4 producing T cells can occur independently of CD28, indicating functional redundancy among costimulatory molecules in type 2 immunity.