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Phenotypic and functional separation of memory and effector human CD8+ T cells
1Department of Clinical Viro-Immunology, Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, University of Amsterdam.
Insights
Researchers identified two distinct human CD8+ T cell subsets: CD45RA-CD45R0+ cells resembling memory T cells and CD45RA+CD27- cells acting as effector cytotoxic T lymphocytes (CTLs). This clarifies human CD8+ T cell populations.
Area of Science:
- Immunology
- Cell Biology
Background:
- Human CD8+ T cell subsets, including memory and effector types, remain poorly defined.
- Understanding these distinct T cell populations is crucial for immune response research.
Purpose of the Study:
- To delineate and characterize distinct memory- and effector-type subpopulations within circulating human CD8+ T cells.
- To identify unique phenotypic and functional markers for these subsets.
Main Methods:
- Flow cytometry analysis of human peripheral blood CD8+ T cells using markers such as CD45RA, CD45R0, CD95, CD27, and CD28.
- Functional assays including cytokine secretion (IL-2, IFN-γ, TNF-α, IL-4), cytolytic activity, and assessment of cytotoxic T lymphocyte (CTL) precursor presence.
Main Results:
- Two discrete primed CD8+ T cell subpopulations were identified: CD45RA-CD45R0+ cells (memory-like) and CD45RA+CD27- cells (effector-like).
- CD45RA-CD45R0+ cells expressed memory markers, secreted multiple cytokines, and contained CTL precursors.
- CD45RA+CD27- cells exhibited effector CTL characteristics, including high cytolytic activity, perforin/granzyme B expression, and Fas-ligand mRNA, with cytokine production limited to IFN-γ and TNF-α.
Conclusions:
- Human CD8+ T cell memory and effector functions can be distinguished as separate subpopulations based on distinct phenotypes and functions.
- The identified subsets, CD45RA-CD45R0+ and CD45RA+CD27-, provide a clearer definition of circulating human CD8+ T cell compartments.
Abstract:
Human CD8+ memory- and effector-type T cells are poorly defined. We show here that, next to a naive compartment, two discrete primed subpopulations can be found within the circulating human CD8+ T cell subset. First, CD45RA-CD45R0(+) cells are reminiscent of memory-type T cells in that they express elevated levels of CD95 (Fas) and the integrin family members CD11a, CD18, CD29, CD49d, and CD49e, compared to naive CD8+ T cells, and are able to secrete not only interleukin (IL) 2 but also interferon gamma, tumor necrosis factor alpha, and IL-4. This subset does not exert cytolytic activity without prior in vitro stimulation but does contain virus-specific cytotoxic T lymphocyte (CTL) precursors. A second primed population is characterized by CD45RA expression with concomitant absence of expression of the costimulatory molecules CD27 and CD28. The CD8+CD45RA+CD27- population contains T cells expressing high levels of CD11a, CD11b, CD18, and CD49d, whereas CD62L (L-selectin) is not expressed. These T cells do not secrete IL-2 or -4 but can produce IFN-gamma and TNF-alpha. In accordance with this finding, cells contained within this subpopulation depend for proliferation on exogenous growth factors such as IL-2 and -15. Interestingly, CD8+CD45RA+CD27- cells parallel effector CTLs, as they abundantly express Fas-ligand mRNA, contain perforin and granzyme B, and have high cytolytic activity without in vitro prestimulation. Based on both phenotypic and functional properties, we conclude that memory- and effector-type T cells can be separated as distinct entities within the human CD8+ T cell subset.