1. Briefly describe the composition and main functions of the immune system:
The immune system is composed of immune tissues and organs, immune cells and immune molecules.
1. Immune organs:
① Central immune organs: bone marrow, supracavitary bursa (birds), thymus; it is the place where immune cells occur, differentiate, develop and mature.
② Peripheral immune organs: lymph nodes, spleen, and mucosa-associated lymphoid tissues; they are the places where immune cells such as mature T and B cells settle, and where immune responses are generated.
2. Immune cells: cells that participate in or are related to the immune response are called immune cells.
① Lymphocytes: T lymphocytes, B lymphocytes, K cells, NK cells, N cells, D cells, etc.;
② monocytes; ③ macrophages; ④ granulocytes : neutrophils, eosinophils and basophils; ⑤ mast cells ; 3. Immune molecules: including complement, lysozyme, betalysin, interferon, immunoglobulin, lymphokine, monokine, thymus factor, etc.
The main functions of immunity: immune defense, immune surveillance, immune homeostasis.
1. The composition and main functions of the immune system
The immune system is composed of immune organs, immune cells and immune molecules.
) Immune organs: bone marrow, spleen, lymph nodes, tonsils, Peyer's lymph nodes, appendix, thymus, etc.
2) Immune cells: lymphocytes, mononuclear phagocytes, neutrophils, basophils, eosinophils, mast cells
cells, platelets, etc.
) Immune molecules: complement, immunoglobulin, interferon, interleukin, tumor necrosis factor and other cytokines. A sound immune system mainly has three major functions of defense, stability and monitoring:
1) Defense function: protect the body against the invasion of pathogens and their toxic products, help the body eliminate foreign bacteria and viruses, and protect people from infectious diseases. When this function is too hypersensitive, hypersensitivity reactions will occur; immunodeficiency diseases;
2) Stability (cleaning) function: human tissue cells are constantly metabolizing, and the immune system can identify old and dead cells in time and remove them from the body, thereby maintaining the stability of the human body. This function is abnormal Autoimmune disease occurs when;
3) Monitoring function: The immune system has the function of timely identifying, killing and clearing cells with chromosomal aberrations or gene mutations to prevent the occurrence of tumors and cancers. When this function is abnormal, persistent infections will not be cleared in time. cannot be contained in time
2. Briefly describe the basic structure and biological function of antibodies:
1. The basic structure of Ig: Ig is a tetrapeptide chain structure composed of two identical heavy chains and two identical light chains connected by interchain disulfide bonds. The amino acid changes in the 1/4 or 1/5 region near the N-terminus of the heavy chain or light chain are called variable regions (V regions); the rest are called constant regions (C regions).
2. The biological functions of Ig include: ①Specific binding to antigen: in vivo, it shows immune effects such as antibacterial, antiviral, and antitoxin; in vitro, antigen-antibody reaction can occur. ②Activation of complement: After IgG and IgM antibodies bind to antigens, they can activate complement through the classical pathway. ③ Binding to cells: Ig binds to Fc receptors on the surface of various cells through the Fc segment, exerts opsonization and ADCC functions, and mediates type I hypersensitivity reactions. ④Cross the placenta and mucous membrane: IgG can cross the placenta and enter the fetus, and SIgA is an important factor for local mucosal anti-infection.
1. Specific binding to the corresponding Ag
2. Activation of complement - IgM.IgG1.IgG2.IgG3
3. Binding to Fc receptors
4. The regulation of antibodies is multi-purpose
1. Conditioning effect
2.ADCC—antibody-dependent cell-mediated cytotoxicity
3. Mediated type I hypersensitivity 4. Passed through the placenta. Mucous membrane
3. Briefly describe the characteristics of various types of immunoglobulins:
Immunoglobulin (Ig) includes five classes of IgG, IgM, IgA, IgD, and IgE, and their characteristics are as follows:
(1) IgG is a standard monomer molecule, which is the main antibody of the second immune response, and has the functions of phagocytosis, opsonization, and neutralization of toxins. , neutralizing viruses, mediating ADCC, activating the classical pathway of complement, etc., can pass through the placenta. IgG is synthesized fast, decomposed slowly, and has a long half-life. It has the highest content in the blood, accounting for 65% to 75% of the total serum Ig content.
(2) IgM is a pentamer, which is the earliest antibody synthesized and secreted in the process of individual development. It is the one with the largest molecular weight among Ig. The molecular structure is circular and contains a J chain. The ability of IgM to agglutinate antigen is much greater than that of IgG, the ability to activate complement is 1000 times higher than that of IgG, and it has phagocytosis and opsonization with complement. Its blood content is low, its half-life is short, it appears early, disappears quickly, and its tissue penetration is weak.
(3) IgA is divided into serotype and secretory type. Serotype IgA mainly exists in monomer form, accounting for 15% to 25% of the total serum Ig content. , to remove large amounts of antigen in a non-inflammatory manner. Secretory IgA (SIgA) is a dimer, each SIgA molecule contains a J chain and a secretory piece, mainly present in gastrointestinal and bronchial secretions, colostrum, saliva and tears. SIgA has stable performance and high local concentration, can inhibit the adhesion of pathogens and harmful antigens to the mucosa, has opsonophagocytosis and dissolution, and constitutes the first-line defense mechanism of the mucosa; secretory IgA in breast milk provides infants with 4-4 to 4-year-old infants. Partial immune barrier within 6 months.
(4) The molecular structure of IgD is very similar to that of IgG, and its performance is unstable. The content in normal human serum is very low and can hardly be detected. The role of serotype IgD is not clear. Cells only express mIgM, mature B cells express both mIgM and mIgD, and mIgD on B cells and memory B cells gradually disappears after activation.
(5) IgEIt is a monomeric structure, and the serum content of normal people is the lowest, which is related to individual heredity and antigen quality. The IgE level in the serum of atopic allergy and parasite infection patients increases, and its Fc segment can interact with mast cells and basophils Binding to receptors on the surface mediates the occurrence of type I allergic reactions, also known as pro-cell antibodies. IgE cannot activate complement.
three,
Compare the similarities and differences of the three pathways of complement:
There are classical pathway, MBL pathway and alternative pathway for the activation of the complement system. Their similarities are as follows: once C3 convertase is formed, C3 is cleaved to form C5 convertase, and C5 is cleaved successively, and then other components of complement are activated in turn to form Membrane attack complex C5b ~ 9 causes cell membrane rupture. Cell death.
5. Briefly describe the biological function of complement:
①Complement-mediated cell lysis; ②Biological effects mediated by active fragments of complement: opsonization; inflammatory response; clearance of immune complexes; immune regulation.
The common terminal effect of complement activation is to mediate cell lysis. At the same time, a variety of cleavage fragments are generated during complement activation, which mediate various biological functions by binding to corresponding receptors on the cell membrane. ①Bacteriolysis and cytolysis: After the complement system is activated, MAC is formed on the surface of the target cell, which leads to the lysis of the target cell ②Opsonization: C3b, C4b, and iC3b produced during complement activation are all important opsonins, which can combine with neutral Corresponding receptors on the surface of granulocytes or macrophages. Therefore, the activation of complement on the surface of microbial cells can promote the combination of microorganisms and phagocytes, and be phagocytized and killed. ③Immune adhesion: C3b produced during complement activation binds to the antibody of the immune complex, and C3b can also bind to blood cells expressing C3b receptors, and be transported to the liver through the bloodstream to be cleared. ④Inflammatory mediators C3a and C5a produced during complement activation. They are also called anaphylatoxins, which bind to receptors on the corresponding cell surface, stimulate cell degranulation, and release vasoactive substances such as histamine, thereby enhancing vascular ventilation . Permeability and stimulation of visceral smooth muscle contraction. C5a is also a potent neutrophil chemokine.
6. Briefly describe the common characteristics of cytokines:
①Cytokines are usually secreted glycoproteins with low relative molecular mass (15-30kD); ②Natural cytokines are secreted by cells activated by antigens, mitogens or other stimuli; ③Cytokines usually act in a non-specific manner ④Cytokines have extremely strong biological effects, and a very small amount of cytokines can produce significant biological effects on target cells; ⑤The production and effects of cytokines are multi-source and multi-directional ⑥Cytokines have pleiotropic, overlapping, antagonistic and synergistic effects when they act, thus forming a complex network; ⑦Mostly exert their effects locally or remotely in the form of paracrine and (or) autocrine and endocrine.
7. Distribution and function of HLA class Ⅰ and class Ⅱ molecules:
1. HLA class I molecules are widely distributed on the surface of all nucleated cells, including platelets and reticulocytes. Class I molecules have not been detected in a few cells such as trophoblast cells at a certain stage of differentiation, nerve cells and mature red blood cells.
The function of HLA class I molecules is mainly to recognize and present endogenous antigenic peptides, and then activate CD8﹢CTL, and its α3 domain can bind to the co-receptor CD8 molecule of CTL, which can enhance the transduction of activation signals. At the same time, HLA class I molecules restrict the recognition and killing of target cells by CTLs.
2. HLA class II molecules are mainly distributed on the surface of antigen-presenting cells such as monocytes/macrophages, dendritic cells and B cells.
The function of HLA class II molecules is mainly to recognize and present exogenous antigenic peptides, thereby activating CD4+Th, and the β2 domain of its β chain can bind to the co-receptor CD4 molecule of Th, which can strengthen the activation signal transduction. HLA class Ⅱ molecules also restrict the interaction between Th and APC, Th and other T cell subsets.
8. Briefly describe the main subsets of T cells and their functions:
T cell subsets: 1. Classified according to the activation stage of T cells (naive T cells, effector T cells, memory T cells); 2. Classified according to TCR types (TCRαβT cells, TCRγδT cells); 3. According to CD molecules Different (CD4+T cells and CD8+T cells); 4. Classified according to different functions (Th, CTL, Treg cells).
Function of T cells: CD4+T cells differentiate into Th0 cells after being stimulated by antigens, and ThO cells are further differentiated into Th1, Th2, Th3 and Th17 subgroups under the stimulation of different cytokines; the main function of Th1 cells is to enhance phagocyte-mediated The main function of Th2 cells is to induce and promote the humoral immune response mediated by B cells; the main function of CD8+CTL cells is to specifically and directly kill target cells.
T cells are divided into several subgroups: helper T cells (Th), which have the function of assisting humoral immunity and cellular immunity; suppressor T cells (Suppressor T cells, Ts), which have the function of suppressing cellular immunity and humoral immunity ; Effector T cells (Te), with the function of releasing lymphokines; Cytotoxic T cells (Killer T cells, Tc), with the function of killing target cells; Delayed allergic reaction T cells (Td), with Participate in the role of type IV allergy; amplify T cells (Ta), which can act on Th and Ts, and have the effect of expanding immune effects; Virgin or Natural T cells (Virgin or Natural T cells), they differentiate into effectors after contact with antigens T cells and memory T cells; memory T cells (Tm), have the effect of memory-specific antigen stimulation.
Biological functions of T cells: directly kill target cells, help or inhibit B cells to produce antibodies, respond to specific antigens and mitogens, and produce cytokines
9. Briefly describe the main ways of antigen presentation (two):
1. The process by which MHC class I molecules present endogenous antigens
Endogenous antigens refer to antigens synthesized in cells, such as intracellular proteins, nucleoproteins, and viral proteins synthesized by virus-infected cells. After these antigens are synthesized in the cell, they are first degraded into small molecular peptides under the action of proteosomes in the cytoplasm. The size of these peptides composed of about 8 to 11 amino acids is similar to the groove of the peptide binding region of MHC class I molecules. .Transferred to the cavity of the endoplasmic reticulum under the action of the transporter associated with antigen processing (TAP), and combined with the newly assembled MHC class I molecules to form antigen peptide-MHC class I molecule complexes. It is then transported to the surface of the cell membrane through the secretory pathway and presented to CD8+ T cells.
2. The process by which MHC class Ⅱ molecules present exogenous antigens.
Exogenous antigens refer to antigens from outside cells. When exogenous antigens enter the body, most of the antigens are taken up by antigen-presenting cells into the cytoplasm by phagocytosis, endocytosis, and receptor-mediated endocytosis. It is hydrolyzed by proteases in endosomes and lysosomes into antigenic peptide fragments that can bind to MHC class II molecules. The newly synthesized MHC class II molecules in the endoplasmic reticulum combine with the antigen peptide to form a stable antigen peptide-MHC class II molecule complex, which is then transported to the surface of the cell membrane and presented to CD4+ T cells.
10. Briefly describe the dual signals of T and B cell activation:
Dual signals of T cell activation: 1. The first signal of T cell activation: TCR specifically recognizes the antigen peptide bound in the groove of MHC molecules 2. The second signal of T cell activation: APC and various adhesion molecules on the surface of T cells Binding to (such as B7/CD28, LFA-1/ICAM-1 or ICAM-2, CD2/LFA-3, etc.). CD28/B7 is an important co-stimulatory molecule involved in the activation of T cells.
Dual signals for B cell activation: 1. BCR antigen receptor complex-antigen epitope 2. Costimulatory molecules, most importantly CD40-CD40L, provide a second signal for B cells.
11. Briefly describe the general rules of B cell response to TD antigen:
Features of TD antigen immune response: 1. Can cause humoral immune response and cellular immune response; 2. Produce various types of antibodies such as IgG; 3. Can induce immune memory.
1. (1) General rules of antibody production
First-response and repeat-response patterns. The primary response refers to the immune response caused when the antigenic substance enters the body for the first time. The characteristics are: ①Long incubation period, and it takes a long incubation period (1-2 weeks) for antibodies to appear in the serum; ②Low antibody titer; ③Short maintenance time in the body; ④IgM -based antibodies; ⑤Low antibody affinity. Re-response refers to the immune response caused by the same antigenic substance entering the body again. The characteristics are: ①short incubation period; ②high antibody titer; ③long maintenance time in vivo; ④antibodies are mainly IgG, while IgM content is similar to the initial response; ⑤high antibody affinity.
(2) Sequence law
In an immune response, the order in which various antibodies are produced is IgM, IgG, IgA, IgD, and IgE. This is consistent with the sequence of Ig production in ontogeny.
2. Initial response : the first time an appropriate amount of antigen is used to immunize animals, and its characteristics are: ①Long incubation period for the emergence of antibodies; ②Low antibody concentration; ③Low plateau and short time; ④Shorter decline period; Large; ⑥The antibody produced is mainly IgM; ⑦The antibody affinity is low.
Re-response: When the same antigen is immunized again during the antibody decline period, the characteristics are: ①short incubation period; ②rapid increase in antibody concentration; ③rapid plateau,
Re-response: When the same antigen is immunized again during the antibody decline period, the characteristics are: ①short incubation period; ②rapid increase in antibody concentration; ③rapid plateau,