What Is T-Cell Immunity?

T lymphocytes are derived from pluripotent stem cells of the bone marrow (from the yolk sac and liver during embryonic period). During human embryonic and nascent stages, part of the pluripotent stem cells or pre-T cells in the bone marrow migrate into the thymus, differentiate and mature under the induction of thymus hormones, and become T cells with immune activity.

T lymphocytes (T lymphocytes) are short for T cells. They are derived from bone marrow-derived lymph stem cells. After differentiation and maturation in the thymus, they are distributed throughout the immune organs and tissues of the body through lymph and blood circulation. ^[1]

Pluripotent stem cells transform into lymphoid precursor cells (Lymphoid precursors) and migrate to the thymus. Under the induction of thymosin, they undergo a series of orderly differentiation processes and gradually mature in the thymus into a T cell bank that recognizes various antigens. T lymphocytes first undergo two stages after entering the thymus: Early T lymphocyte development stage, that is, the ancestor CIM and CD8 double negative cell (DN) differentiate into CD4 and CD8 double positive cell (double positive cell) , DP); DP cells undergo positive selection phase and negative selection phase to acquire MHC restricted recognition ability and tolerance to self-antigens, and develop into single positive T cells (single positive cell (SP) whose surface marker is CD4 or CD8. ), Settled in the surrounding lymph organs ^[2]

T cells are quite complex and heterogeneous, and they are constantly renewed in the body.There can be different developmental stages or functions at the same time.

1. T cell antigen receptor (TCR): TCR is a specific receptor that T cells recognize and bind to foreign antigens, and can be expressed on the surface of all mature T cells. The TCR molecule of most mature T cells (about 95%) is composed of two heterodimer peptide chains, chain and chain, and a small part is composed of and chains. During the development of T cells, genes encoding and determine the high polymorphism of TCR. Different T cell clones have different TCRs and can recognize different epitopes (determinants). TCR cannot directly recognize and bind free soluble antigens. It only recognizes antigen molecules that are processed by antigen presenting cells and linked to MHC molecules. TCR cannot directly activate T cells after binding to the antigen. It needs to rely on its neighboring CD3 molecules to pass into the cell. Activation information, CD4 and CD8 synergize and enhance this effect.

2. Mitogen Receptor: Mitogen can activate resting lymphocytes into lymphoblasts through corresponding receptors, which stimulates the proliferation and differentiation of polyclonal T and B cells. It mainly includes phytohemagglutinin (PHA), concanavalin A (ConA), lipopolysaccharide (LPS), pokeweed mitogen (PWM), staphylococcal protein A (SPA) and polymerized flagellin.

3. E receptor (CD2): exists on the surface of peripheral T cells and thymus cells, can bind to sheep red blood cells, is an adhesion molecule, is a lymphocyte function related antigen-2 (LFA-2), and its ligand is antigen presentation LFA-3 on cells and other target cells promotes the binding and interaction of T cells with antigen-presenting cells and induces activation.

4. CD3: It exists on the surface of peripheral blood T cells and part of thymocytes. It forms a TCR-CD3 complex molecule with TCR and transmits the antigen signal into the cell.

5. CD4 and CD8: Pre-thymic cortex T cells can express both CD4 and CD8, and peripheral blood T cells express only one of these molecules. CD4 and CD8 bind to MHC-II and MHC-1 molecules, respectively, and stabilize the binding of TCR to the antigen peptide-MHC molecule complex, which helps to activate signal transmission. CD4 molecule is the main receptor for HIV to enter target cells, so HIV selectively destroys CD4 + cells, resulting in acquired immune deficiency.

6. CD5 antigen: It is present on all peripheral blood T cells, and CD5 is expressed on a small part of B cells and chronic B lymphocytic leukemia cells. Anti-CD5 antibodies can enhance the proliferative response of mitogens to T cells.

7. CDll a / 18: Also known as LFA-1, the ligands are intercellular adhesion molecule-1 (ICAM-1) and intercellular adhesion molecule-2 (ICAM-2), which cooperate to stimulate signals to induce T cell activation.

8. CD28: Its ligand is B, a molecule on the surface of antigen-presenting cells. The combination of the two produces a synergistic stimulus signal and induces T cell activation.

9. HLA Antigen: Peripheral blood T cells in the resting state only express HLA-I antigens, and some activated T cells can simultaneously express I and II antigens.

lo, interleukin receptors: T cells express different interleukin receptors (IL-R) at different developmental stages, such as IL-1 R, IL-2R, IL-4R, and IL-6R, etc. ^[2]

T cells are the main components of lymphocytes, and they have a variety of biological functions, such as directly killing target cells, assisting or inhibiting B cells to produce antibodies,

In early January 2013, Japanese scientists for the first time produced T cells that could kill cancer cells. They said the research breakthrough paved the way for direct injection of T cells into cancer patients to fight cancer. In fact, the body can produce T cells naturally, but in smaller numbers. The successful cultivation of T cells makes it possible to inject such cells in large quantities into patients to strengthen the immune system.

In order to cultivate such cells, they first "reprogrammed" T lymphocytes that specifically kill a certain type of cancer cell, turning them into another type of cells, called "inducible pluripotent stem cells". The pluripotent stem cells then develop into fully functional T lymphocytes. T lymphocytes developed from induced pluripotent stem cells may serve as a potential cancer treatment in the future.

Japanese scientists cultivate T lymphocytes that specifically fight a type of skin cancer into induced pluripotent stem cells by exposing the lymphocytes to a "Yamanaka factor" environment. Yamanaka factors are a group of compounds that bring cells back to the "non-professional" stage. In the laboratory, researchers turned induced pluripotent stem cells into T lymphocytes. Like the original T lymphocytes, the T lymphocytes at this time also specialized in the same skin cancer. They have the same genetic makeup as the original T lymphocytes and are capable of expressing cancer-specific receptors. Studies have found that this new type of T lymphocyte is very active and can produce an anticancer compound.

Dr. Kawamoto said, "We successfully cultivated T cells with specific antigens by culturing induced pluripotent stem cells and then turning them into functional T cells. The next step is to study whether these T cells are selective Kill cancer cells or kill them together with other cells. If you selectively kill cancer cells, these T cells can be directly injected into patients to fight cancer. In the not too distant future, we can implement this for cancer patients A therapy. "The findings are published in"

1. Induction phase:

T cells

Target cell pair

I. Phenotypic changes of T cells during thymic differentiation

Lymphatic stem cells are present early

CD4 and CD8 monoclonal antibodies can be used to divide T lymphocytes in peripheral lymphoid organs or peripheral blood into two major subgroups: CD4, CD8- and CD4-CD8. Each subgroup can be divided into different functional subgroups according to some surface signs and functions. CD4 positive cell population

Using different Th cell clone culture techniques and cytokine production, mouse CD4-positive cell populations have been found to be an uneven subpopulation that can be divided into Th1 and Th2. The main differences are shown in Table 7-6.

Th1 cells can synthesize IL-2, IFN-, LT, IL-3, TNF-, and GM-CSF, but cannot synthesize IL-4, IIL-5, IL-6, IL-10, and IL-13; Th2 can synthesize TNF-, IL-3, GM-CSF, IL-4, IL-5, IL-6, IIL-10 (cytokine synthesis inhibitor, CSIF) and IL-13, but cannot synthesize IL-2 , IFN- and LT. In addition, Th1 and Th2 can secrete three macrophage inflammatory proteins and proenkephalin. Both Th1 and Th2 help B synthesize antibodies, but the strength and nature of the help are different. In vitro experiments show that IL-4 significantly promotes B cell synthesis and secretion of IgE, such as increasing the ability of LPS to stimulate mouse B cells to synthesize IgE by 10-100 times. A small amount of IFN- can completely obliterate the promotion effect of IL-4 on IgE synthesis. Th2 secretes IL-4, which positively regulates IgE synthesis, while Th1 secretes IFN-, which negatively regulates. In addition, Th2 secretes IL-4 and IL-5 to assist in the synthesis of IgA, secretes IL-10 (CSIF), and inhibits the synthesis of cytokines in Th1 cells, while Th1 inhibits the synthesis of IgG1, but assists the synthesis of other types of Ig . Because Th1 and Th2 synthesize lymphoid factors, they mediate different hypersensitivity reactions. Both IL-3 and IL-4 can promote the proliferation of mast cells and have a synergistic effect. In addition to assisting B cells in synthesizing IgA, IL-5 can also stimulate the formation of bone marrow eosinophils. Therefore, Th2 and fast-type hypersensitivity The response is close. Th1 blocks IgE synthesis by producing IFN-, and has an inhibitory effect on immediate hypersensitivity. Th1 is related to delayed type hypersensitivity, and may be related to IL-2, IFN- and other effects on macrophage activation and promotion of CTL differentiation. In addition, LT also has a direct killing effect on target cells. Both groups of Th clones were able to induce antigen-presenting cells (APC) to express MHC class II antigens, Th1 induced M to express Ia antigen through IFN-, and Th2 positively regulated the expression of M and B cell Ia antigens through IL-4. Subgroups of human Th1 and Th2 cells have not yet been confirmed. According to published data, CD4 CD45RO precursor cells differentiate into Th2 effector cells, while IFN- inhibits the differentiation of precursor cells into Th2. Therefore, IL-4 and IFN- determine the orientation of CD4 CD45RO precursor cells. Th1 or Th2 plays an important regulatory role in the differentiation process. After polyclonal activation of human T cells, the IL-4 mRNA-positive ratio in CD4-positive cells was less than 5%, and 60% of CD4 cells had IFN- and IL-2 mRNA transcription.

Suppressor-inducing subpopulations and helper-cell-inducing subpopulations CD45RA, CD45RO, CD29, and CD31 monoclonal antibodies can be used to divide CD4-positive cell populations into suppressor-inducible and helper-cell-inducible subpopulations.

CD31: CD31 was found to be a new surface marker that induces a subpopulation of suppressor cells that does not change significantly after activation. CD31 is a platelet-endothelial cell adhesion molecule (PECAMgpa) with a molecular weight of 140 kDa, and its structure belongs to a member of the immunoglobulin superfamily. Among the freshly isolated CD4 cells from peripheral blood, CD31McAb mainly reacts with the CD45RA subpopulation, has no obvious auxiliary effect on IgG synthesis by B cells, and is more sensitive to ConA and its own MHC (self MLR) response; while in CD31-CD4 cell population, It was found that a large number of helper B cells synthesize IgG activity and recall response to certain antigen stimulation. After the large activation of CD4 cells of CD45RA, although the surface of CD45RA was lost, the expression of CD31 on the surface did not change significantly; CD45RO CD45RA-CD4 cells could not obtain CD31 expression after activation. Since CD31 does not change after CD4 cells are activated, it is a useful marker for identifying suppressor subpopulations and helper cell subpopulations.

Many adhesion molecules such as CD11a / CD18 (LFA-1) LFA-3, CD2 and CD29 (VLA chain) are mainly expressed on the surface of CD45RO T cells. CD31 is expressed on the surface of CD45RA CD4 cells. Anti-CD31McAb on naiveT cells can trigger its VLA-4 mediated adhesion. The interaction of CD31 and its ligands on endothelial cells with CD31 and its ligands on T cells is likely to trigger integrin-mediated adhesion. How CD31 participates in CD45RA CD4 T cell function and induces suppressor T cell production remains to be further studied.

CD45: CD45 is an isomeric molecule. CD45 cell membrane external polypeptide chain can be encoded by three exons A, B and C. Human naive T cells only express the CD45A type recognized by anti-CD45RA; memory T cells do not express any A, B, and C exon products and are recognized by anti-CD45RO. Both anti-CD45RA and anti-CD45RO recognize resting cells. Memory T cells recognized by anti-CD45RO can also express a series of activated surface markers at low levels, such as CD25, MHC class II antigen, CD54, CD26, etc., suggesting that such cells may be Recently activated, it is deduced that memory T cells may maintain their long-term survival due to low doses of persistent antigens or cross-antigens and sustained stimulation. In vitro experiments observed a unidirectional transition from CD45RA to CD45RO after cell activation, which is parallel to the differentiation of naive T cells into memory T cells.

(3) Self-Mixed Lymphocyte Reaction: Non-T cells such as peripheral blood B cells and monocytes can induce the proliferation of certain auto-T cells when cultured in vitro, which is called autologous mixed lymphocyte reaction (AMLR). These T cells are called autoreactive T cells. B cells and monocytes, which are stimulating cells, stimulate self-reactive T cells mainly by MHC class II antigens on their cell surface. Adding antibodies against MHC class II antigens in vitro can block AMLR. May be an immune regulating mechanism of the body.

CD8 positive cell population

According to CD28 positive or negative, CD8 cells can be divided into cytotoxic T cells (CD8 CD28 +) and suppressor T cells (CD8 CD28-). CD28McAb can react with 60-80% T cells, including all CD4 cells and some CD8 cells.

Phenotype in human CTL is CD3 CD4-8 CD28. Mouse CTL phenotypes are Thy-1, Lyt-1, Lyt-2 / Lyt-3.

CTL differentiation: The stationary CTL precursor (CTL-P) exists, and the foreign antigen enters the body and is processed by the antigen presenting cell (APC) to form a complex of the foreign antigen and the APC's own MHcI class antigen. Under the condition that TCR / CD3 is recognized on the surface of the cell membrane of the corresponding CTL clone, under the condition that the antigen-stimulating signal and IL-1 released by APC coexist, CTL-p is activated and expresses a variety of cytokines such as IL-2R, IL-4R, IL-6R Receptors, induced by cytokines such as IL-2, IL-4, IL-6, and IFN-, rapidly proliferate and differentiate into mature effector killer T cells (effectorCTL). CTLs have the specificity of recognizing antigens, that is, they can kill target cells with a complex of specific foreign antigens (such as viral antigens on the surface of infected cell membranes) and their own MHcI class antigens. The target cells for killing CTLs are restricted by MHCI-like antigens. CTL isolated from tumor tissues is called tumorinfiltratinglymphocyteTIL. TIL has a high tumor-killing effect after being cultured in vitro with IL-2, and has been used in clinical tumor treatment.

CTL recognition mechanism: a variety of adhesion molecules participate in the recognition and adhesion of CTL to target cells, mainly: LFA-1 / ICAM-1, ICAM-2, ICAM-3, soluble ICAM-1 (sICAM-1) can Inhibition of CTL killing tumor cells; CD2 / LFA-3 (CD58), anti-CD2McAb or anti-CD58McAb can inhibit the killing of target cells by CTL effector cells; non-polymorphic domains of CD8 / MHcI class antigens.

CTL killing mechanism: TCL killing target cells is believed to be mediated through the release of multiple mediators and factors.

Perforin: also known as pore-foming protein (PFP), C9 related protein (C9 related protein) or cytolysin (cytolysin), stored in electron dense cytoplasmic particles (electron-densecytoplasmicgranules), mature perforation The molecule consists of 534 amino acid residues with a molecular weight of 56-75kDa and an IP of 6.4. The amino acid sequence between the central portion of the perforin molecule 170-390 and the C9328-560 amino acid sequence have about 20% homology. This Regions are associated with multimerization of perforin and C9 and insertion into the cell membrane in a tubular form. During the killing phase, CTL cells are degranulated, and perforin is released from the particles. In the presence of Ca2, it is inserted into the target cell membrane and polymerized to form a tubular polyperforin, which contains about 12-16 perforins. Molecule with molecular weight up to 1000kDa. Polyperforin forms a membrane-perforating tubular structure on the target cell membrane with an average inner diameter of 16 nm. This abnormal channel allows Na and water to enter the target cell, and K and macromolecular substances (such as protein) flow out from the target cell, which changes the osmotic pressure of the cell and eventually causes the cell to lyse. This process is similar to complement-mediated lysis, which is relatively rapid. CTL itself may release A type of chondroitin sulfate proteoglycan (proteoglycansofchondroitinsulphateAtype) and chondroitin sulfate A restriction factor (HRF), so it can prevent perforin from attacking CTL's own cells.

serineestersse: Activates CTL to release a variety of serine esterases, such as CTLA-1 (also known as CCP1 or granzymeB), CTLA-3 (also known as factor H or granzymeA), and its role may be similar to that during complement activation Esterase action, which promotes killing by activating perforin.

Ts and Ts subpopulation suppressor T cells (suppressor TlymphocyteTs) have important negative regulatory functions on the immune response, abnormalities of suppressor T cells are often related to T autoimmune diseases, type I hypersensitivity and other diseases.

Confirmation of inhibitory T cells: sheep red blood cells (sheepredbloodcellSRBC) are good immunogens for mice, and appropriate doses of SRBC can induce mice to produce high titer anti-SRBC antibodies. When mice were immunized with SRBC at an excessively high dose, the antibody synthesis level decreased significantly, which is called high-dose immune tolerance. Animal experiments have found that when high-dose immune-tolerant mice are transferred to mice stimulated with an immunogen dose, the antibody response level of the mice is significantly reduced. If the spleen cells of high-dose immune-tolerant mice are treated with anti-Thy-1 and complement and then transferred to mice immunized with immunogen doses, the inhibitory effect of spleen cells of high-dose immune-tolerant mice disappears. Experiments have demonstrated the presence of suppressive T cells in spleen cells of high-dose immune-tolerant mice.

The phenotype of this suppressor cell is CD3 CD4-CD8 (mouse CD8 monoclonal antibody Lyt-2 is commonly used). The phenotype of human suppressor T cells is CD3 CD4-CD8 CD28-. Ts cells not only have inhibitory effects on B cell synthesis and secretion of antibodies, but also have negative regulatory effects on Th helpers, delayed hypersensitivity, and Tc-mediated cytotoxicity.

Ts cell subgroups: Ts cells can also be divided into different subgroups of Ts1, Ts2, and Ts3, which play a role in inducing inhibition, transduction inhibition, and exerting inhibitory effects, respectively. The exact mechanism of their interaction is not fully understood, and may be through the release of soluble media. Ts1 (Tsi, antigen-specific inhibitory T cells) secretes TsF1 (TsiF, inhibits induction factor) acts on Ts2 (Tst, inhibits transduced cells), secretes TsF2 (TstF) acts on Ts3 (Tse, inhibits effector cells) , Secretes Ts3F (TseF), acts on Th cells, and through the inhibition of Th, thereby negatively regulating various immune functions. The Ts cell population is highly heterogeneous. In addition to the Ts1, Ts2, and Ts3 subpopulations, there is also a group of anti-suppressor Tcel subpopulations (contra-suppressorTcel, Tcsl). After Tcs activation, the anti-inhibitory T cell factor TcsF is secreted, which directly acts on Th cells, releases the Ts cell inhibitory effect, and restores Th cells to auxiliary activity.