Immunology Cell Identity Markers

Adaptive Immunity

Adaptive immune responses are mediated by cellular (lymphocytes) effectors, soluble (cytokines) effectors, and humoral (plasma cell-derived antibodies) effectors. Versatility and memory are the two main distinguishing properties of the adaptive arm of the immune system. Versatility is underscored by genetic recombination mechanisms which ensure the expression of immune receptors with high specificity for antigen recognition in T and B lymphocytes. Immune memory results from the persistence of long lived lymphocytes with antigen specific receptors and antibody-secreting plasma cells, which are able to mount a rapid immune response upon re-stimulation.

T Cell Subsets

 

Adaptive Cellular Mediators: Functions and Markers

T Cell Subsets Function Markers
Naïve T lymphocytes
 		 Mature T lymphocytes present in the blood and lymphoid organs without previous antigen interaction and thus inactive. Interaction with peptides presented through cells of the innate immune system, such as dendritic cells serving as antigen presenting cells, leads to T cell activation. CD45RA, CD62L, CCR7, CD27, CD28, CD25
Effector T lymphocytes
 

Once activated, naïve CD4+ and CD8+ T lymphocytes generate different cell subsets.
CD8+ subsets: Tc1 and Tc2
CD4+ subsets: Th1, Th2, Th17 and Treg (Foxp3)

 

Activated T cells perform cytotoxic functions via two main mechanisms:

Cell-mediated- via cytotoxic CD8+ T cell induced lysis of damaged cells (infected or transformed)

Soluble factors-mediated- via CD4+ T helper cell dependent release of cytokines that are toxic to infected cells or promote the activity of other immune cells (e.g., increase of antibody production and activity of NK cells)

 CD69, CD25, CD45RO, OX40, 4-1BBL, CD95, Granzyme B, Perforin, CD44

Memory T Cells

Following exposure to an antigen, a small subset of effector T cells differentiate into memory cells and remain for years in peripheral lymphoid and non-lymphoid tissues. Memory T cells maintain their antigen specificity and help to amplify the immune response during antigen re-exposure. Memory T cells conform a heterogeneous population consisting of effector and central memory subsets. Some relevant markers include CCR7, CD62L, CD45RO, CD45RA, CD95, CD127, CD28 and Granzyme B.

CD4 expression in human T cells ICC

CD4 was detected in immersion fixed human T cells using 2 μg/mL Goat Anti-Human CD4 Antigen Affinity-purified Polyclonal Antibody (Catalog #AF-379-NA) for 3 hours at room temperature. Cells were stained (red) and counterstained (green). View our protocol for Fluorescent ICC Staining of Cells on Coverslips.

Intracellular perforin expression in CD8 T cells ICC

Immunocytochemistry/Immunofluorescence: Perforin Antibody (deltaG9) [NBP1-45774] - Isolated CD8 T-cells showing intracellular perforin (green).

Humoral Markers

In addition to the use of CD markers for the identification of T cell subsets, various effector molecules specifically produced and secreted by T cells may facilitate their identification. Several types of cytokines are released from T cell subsets and may play both pro- and anti-inflammatory roles. Cytokines modulate the activity of T and B cells by influencing their growth, mobility and differentiation.

T Cell Subsets Effector Molecules
Th1 IFN-γ, TNF-α, IL-2, Lymphotoxin
Th2 IL-4, IL-5, IL-10, IL-13
Th17 IL-17, IL-21, IL-22, IL-25, IL-26
Treg IL-10, TGF-β
T (CTL) Perforin, Granzymes, IFN-γ, TNF-α, TNF-β

 

γδ T and NK T Cells Bridge Innate and Adaptive Immunity

γδ T cells comprise a relatively small subset of T cells (up to 5% of peripheral blood mononuclear cells). Similar to conventional T cells the smaller subset of γδ T cells is thymus derived, but differs in T cell receptor (TCR) composition, expressing a γδ heterodimer rather than an αβ TCR. γδ T cells may be found in peripheral blood and associated with epithelial tissues, where they play a role in innate immunity recognizing infectious antigens and tumor cells. γδ T cells express natural killer receptors and TCRs, thereby connecting both arms of immunity.

γδ T types Function Effector Molecules and Markers
Vδ1 Mainly found in mucosal epithelium where they provide immune defense against infections and transformed cells IL-10
Vδ2 Predominant subset of peripheral γδ T cells which serve as antigen presenting cells (APCs) MHCII (HLA-DR), CD80, CD86
Vδ3 Not frequently found in blood but may be present in organs (e.g., liver), and may promote maturation of APCs MHCII (HLA-DR), CD56, CD161, NKG2D

 

Natural Killer T cells (NKT) represent a small subtype of circulating T lymphocytes that are functionally similar to both NK and T cells. NKT cells diverge from conventional T cells in TCR expression and recognize CD1d associated lipid antigens. Type I NKT cells represent the more prevalent subset and are characterized by the expression of TCRs with an invariant alpha chain (Vα14–Jα18 ). NKT cells may also be identifiable by expression of CD161, Ly49, NKG2 and CD3 as well as CD44 and CD122 upon activation.

 

Cells of the Innate and Adaptive Immune System

Gamma Delta T and NK T cells bridge innate and adaptive immunity

Cells of the innate immunity branch provide a rapid response to non-self antigens, in contrast cells of the adaptive immunity branch provide a slower but highly specific response. Several cell subsets, including γδ T cells and NKT cells, connect both branches of immunity because they express receptors similar to those in conventional B and T cells. Even though the specificity of these receptor is limited, the response to specific non-self antigens is prompt.

B Cell Subsets

Knowledge about the role of B cells in immunity continues to expand. Traditionally, B cells have been recognized for their unique capacity to produce antibodies, however identification of B cell subtypes with unique functions and localization have clarified B cell contributions to both adaptive and innate immunity. Recently, B cells have been shown to participate in various antibody-independent roles in immunity including:

  • Antigen presentation
  • Cytokine production
  • Modulating the response of other immune cells (e.g., T cells)
  • Tissue repair

Functions and Markers

Adaptive Cellular Mediators

Cell Type Location and Function Markers
Long-lived Follicular B cells Mature B cells present in secondary lymphoid tissues which may give rise to short-lived plasma cells, antibody-secreting plasma cells, and memory B cells. Mice: CD23, CD21, CD1d, CXCR5

Human: CD23, CD21, CXCR5

Plasmablast: CD138 (mice), CD38, CD27

Plasma cells: CD38 (human), CD27, CD138 (mice)

Innate Cellular Mediators

Cell Type Location and Function Markers
Splenic Marginal Zone B cells Mature B cells that interface the circulatory and lymphatic tissues. Provide rapid defense against blood pathogens. IgM and IgG3 antibody responses are elicited by interactions between bacterial antigens and B cell receptors (BCRs) or Toll-like receptors (TLRs).

Mice: CD21, CD1d, CD9, CD35, CD80, CD86

Human: IRTA1, IRTA2, CD1c, CD27, CD21
B1 cells Mature B cell subset present in tissues (e.g., intestine, peritoneal cavity). Responsible for IgM and IgG3 antibody responses following exposure to bacterial antigens and to polysaccharide antigens. Derived from the fetal liver and produce the majority of natural low-affinity IgM antibodies as well as antigen-specific antibodies.

Mice:  CD5, CD43, IL-5R, B220, CD9

Human: CD20, CD27, CD43, CD5

Additional markers include the pan B cell marker CD19.

 

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