Quantifying Antigen-Specific CD4 T Cells during a Viral Infection: CD4 T Cell Responses Are Larger Than We Think

Abstract

The number of virus-specific CD8 T cells increases substantially during an acute infection. Up to 90% of CD8 T cells are virus-specific following lymphocytic choriomeningitis virus (LCMV) infection. In contrast, studies identifying virus-specific CD4 T cell epitopes have indicated that CD4 T cells often recognize a broader array of antigens than CD8 T cells consequently making it difficult to accurately quantify the total magnitude of pathogen-specific CD4 T cell responses. Here we show that following LCMV infection CD4 T cells become CD11ahiCD49d+ and retain this expression pattern into memory. During the effector phase, all of the LCMV-specific IFN-γ+ CD4 T cells display a CD11ahiCD49d+ cell surface expression phenotype. In addition, only memory CD11ahiCD49d+ CD4 T cells make IFN-γ following stimulation. Furthermore, upon secondary LCMV challenge, only CD11ahiCD49d+ memory CD4 T cells from LCMV-immune mice undergo proliferative expansion, demonstrating that CD11ahiCD49d+ CD4 T cells are truly Ag-specific. Using the combination of CD11a and CD49d, we demonstrate that up to 50% of the CD4 T cells are virus-specific during the peak of the LCMV response. Our results indicate that the magnitude of the virus-specific CD4 T cell response is much greater than previously recognized.

Cytomegalovirus-Specific CD4 T Cells Are Cytolytic and Mediate Vaccine Protection

“…However, Ͼ95% of m78-specific cells show this phenotype (Fig. 3C), indicating that almost all MCMV-specific CD4 T cells will likely be contained in this CD4 T cell compartment, as they are for several other viruses, but not all (41). The majority (Ͼ50%) of CD44 hi CD11a hi CD49d ϩ CD4 T cells in the spleens of MCMV-infected mice were found to display a Th1-like phenotype, producing IFN-␥ and/or TNF-␣, much greater than the ϳ15% observed in naive mice.…”

“…The polyclonal MCMV-specific CD4 T cell response was estimated by CD44 hi CD11a hi CD49d ϩ surface marker expression (41). Representative flow plots depicting the expression profiles of CD11a and CD49d of total CD4 T cells from spleens, livers, and lungs of naive and day 8 MCMV-infected mice are shown in Fig.…”

CD4+T Cells Develop Antiretroviral Cytotoxic Activity in the Absence of Regulatory T Cells and CD8+T Cells

“…Thus, we analyzed the bulk population of virus-specific CD4 ϩ T cells using a combination of CD43 and CD62L staining. It has previously been shown that all CD4 ϩ T cells from FV-infected mice that upregulated the activation-induced glycoform of CD43 (25,26) also expressed CD11a ϩ (27), indicating that they were activated by cognate antigen rather than nonspecific inflammatory modulators (28). We prefer CD43 as a marker for effector T cells because unlike CD11a, CD43 is downregulated upon differentiation into memory T cells (29,30).…”

TGF-β receptor maintains CD4 T helper cell identity during chronic viral infections

“…CD4 T cells differentiate into Th1 and follicular helper (T FH ) subsets during chronic viral infection, and these T helper subsets are critical in maintaining CD8 T cell and B cell responses, respectively. LCMV-specific CD4 T cells can be identified by coexpression of the activation markers CD11a and CD49d during LCMV infection (21 Terminally differentiated Th1 CD4 T cells express PSGL1 + and Ly6C + during acute LCMV infection, and these markers enrich for TBET and granzyme B expression (28). However, during chronic infection Ly6C + effector cells are lost and T FH predominate as a CD4 T cell subset (25,29).…”