CD28 is required for induction and maintenance of immunological memory in toxin-reactive CD4+ T cells in vivo

Area of Science:

• Immunology
• T cell biology
• Molecular mechanisms of T cell survival

Background:

• CD4+ T cells play a central role in adaptive immunity.
• Superantigens, like staphylococcal enterotoxin A (SEA), can induce massive T cell expansion.
• CD28 is a critical co-stimulatory molecule for T cell activation and survival.

Purpose of the Study:

• To investigate the role of CD28 in the in vivo expansion and maintenance of SEA-reactive Vbeta3+ CD4+ T cells.
• To determine the mechanisms underlying T cell population dynamics in the absence of CD28 signaling.

Main Methods:

• Utilized CD28 knockout (CD28-/-) mice and wild-type (C57BL/6) controls.
• Administered SEA via mini-osmotic pumps to induce T cell responses.
• Monitored Vbeta3+ CD4+ T cell populations over 28 days post-implantation.
• Assessed T cell phenotypes, including memory markers and Th2 deviation.
• Analyzed apoptosis induction and expression of anti-apoptotic proteins (Bcl-2, Bcl-xL).

Main Results:

• In CD28-/- mice, Vbeta3+ CD4+ T cells expanded similarly to wild-type mice initially but then rapidly declined by day 28.
• The remaining T cells in CD28-/- mice lacked memory phenotypes and Th2-deviated responses.
• The decline was attributed to upregulated apoptosis, linked to reduced Bcl-2 and Bcl-xL expression.

Conclusions:

• CD28 is essential for the sustained expansion and maintenance of SEA-reactive CD4+ T cells in vivo.
• The absence of CD28 signaling promotes T cell apoptosis, impairing the generation of long-lived memory T cells.
• These findings underscore the critical role of CD28 co-stimulation in adaptive immune responses.