Immunopathology

immunopathology

1. IMMUNOPATHOLOGY Presented by Dr. Vamshikrishna Dussa Dept of Pathology

2. Immunity and immunopathology are proverbial two edges of ‘double-edged sword ’ i.e. it is a defense mechanism but it can be injurious to the human body in a variety of ways. Immunity or body defense mechanism is divided into 2 types: Natural (innate) Specific (adaptive) which are interlinked to each other in their functions

3. ATTRIBUTE INNATE IMMUNITY ADAPTIVE IMMUNITY ACTIVATION ACTIVE PRIOR TO EXPOSURE TO ANY MICROBE OR ANTIGEN ACTIVATED BY EXPOSURE TO ANY MICROBES OR ANTIGENS RESPONSE IMMEDIATE, NO LAG PHASE TAKES TIME FOR RESPONSE SPECIFICITY NO SPECIFICITY, TARGETS ALL PATHOGENS HIGHLY SPECIFIC, TARGETS SPECIFIC PATHOGENS. MEMORY NO IMMUNOLOGICAL MEMORY IMMUNOLOGICAL MEMORY SEEN EXAMPLES Neutrophils, Macrophages, And Natural Killer (NK) Cells . Antibodies

4. Natural or Innate immunity It has 2 major components: Humoral: complement proteins, cytokines, Cellular: Neutrophils, Macrophages, and Natural killer (NK) cells, Dendritic cells.

5. Specific or Adaptive immunity It is specific and is characterized by antigenic specificity. It too has 2 main components: a) Humoral: consisting of antibodies formed by B cells. b) Cellular: mediated by T cells.

6. HUMORAL AND CELL MEDIATED IMMUNITY IN ADAPTIVE IMMUNITY

7. The major functions of immune system are as under: i ) Recognition of self from non-self ii) Mounting a specific response against non-self iii) Memory of what was earlier recognised as non-self iv) Antibody formation v) Cell-mediated reactions

8. While normal function of immunity is for body defense, its failure or derangement in any way results in diseases of the immune system which are broadly classified into the following 4 groups: 1-Immunodeficiency disorders 2- Hypersensitivity reactions 3- Autoimmune diseases 4- Idiopathic immune disorders

9. IMMUNE SYSTEM WHEN NORMAL BODY DEFENSE WHEN ABNORMAL Idiopathic immune reaction Failure of recognition of self and non-self Excessive/ Inappropriate Inadequate Immunity/ Absent Immunity IMMUNO- DEFICIENCY DISORDERS (like AIDS) HYPERSENSITIVITY REACTIONS (like Asthma) AUTOIMMUNE DISORDERS (like RA) AMYLOIDOSIS

10. In any discussion of immunity, a few terms and definitions are commonly used as follows: Antigen (Ag): Usually a substance, usually protein in nature, which when introduced into the tissues stimulates antibody production. Antibody ( Ab ): A protein substance produced as a result of antigenic stimulation. Circulating antibodies are immunoglobulins ( Igs ) of which there are 5 classes: IgG , IgA , IgM , IgE and IgD .

11. Hapten : Non-protein substance which has no antigenic properties, but on combining with a protein can form a new antigen capable of forming antibodies.

12. The antigen may combine with antibody to form antigen-antibody complex. The reaction of Ag with Ab in vitro may be primary or secondary phenomena; the secondary reaction induces a number of processes such as: Agglutination, Precipitation, Immobilisation, Neutralisation, Lysis Complement Fixation. In vivo, the Ag- Ab reaction may cause tissue damage.

13. AGGLUTINATION PRECIPITATION

14. ORGANS AND CELLS OF IMMUNE SYSTEM The organs of immune system are distributed at different places in the body. These are as under: a) Primary lymphoid organs: i ) Thymus ii) Bone marrow b) Secondary lymphoid organs: i ) Lymph nodes ii) Spleen iii) MALT (Mucosa-Associated Lymphoid Tissue located in the respiratory tract and GIT).

15. Anatomical locations of MALT

16. The cells comprising immune system are as follows: i ) Lymphocytes ii) Monocytes and Macrophages iii) Mast cells and Basophils iv) Neutrophils v) Eosinophils

17. Monocytes and Macrophages Circulating monocytes are immature macrophages and constitute about 5% of peripheral leucocytes. They remain in circulation for about 3 days before they enter tissues to become macrophages.

18. Each type of macrophage, determined by its location, has a specific name: MACROPHAGE NAME LOCATION MONOCYTES BONE MARROW/BLOOD KUPFFER CELLS LIVER MICROGLIA CNS OSTEOCLASTS BONE LYSOMAC PEYERS PATCH HISTIOCYTE CONNECTIVE TIVE HOFBAUER CELLS PLACENTA

19. The macrophage subpopulations: Dendritic cells (in the lymphoid tissue) Langerhans ’ cells (in the epidermis) They are similar in morphology and function to  macrophages

20. IMPORTANT IMMUNE FUNCTIONS OF MACROPHAGES: 1. Antigen recognition They possess cell surface receptors to several extracellular molecules: Receptor for Cytokines, Component Of Complement (C3b), Selectin Integrins Fc (Constant Fragment) Of Antibody.

21. RECEPTORS These receptors recognize the organisms and initiate intracellular mechanism in macrophages.

22. Macrophages have capacity to distinguish self from non-self by presence of Human Leucocyte Antigens (HLA) or Major Histocompatibility Complex (MHC)

23. 2. Phagocytosis: Antigen that has been recognized by the macrophages due to availability of above-mentioned surface receptors is ready to be engulfed by the process of cell-eating by macrophages.

24. 3. Secretory function: Macrophages secrete important substances as follows: Cytokines: IL-1, IL-2, IL-6, IL-8, IL-10, IL-12, Tumour Necrosis Factor-α Prostaglandins: PGE, Thromboxane -A, Leukotrienes Cytokines and Prostaglandins which are chemical mediators of inflammation and activate other leucocytes.

25. iii) Secretion of proteins involved in wound healing e.g. Collagenase, Elastase, Fibroblast Growth Factor, Angiogenesis Factor . iv) Acute phase reactants e.g. Fibronectin, Microglobulin, Complement Components.

26. 4. Antigen presentation When macrophages are unable to lyse an antigen or an organism, the next best course adopted by them is to act as antigen-presenting cells for presenting to T cells (subtype CD4+ or CD8+ cells), or to B cells. Accordingly, the lymphoid cell would then deal with such antigen.

27. MACROPHAGE T-CELL (CD4/CD8 CELLS) Antigen presentation

28. Neutrophils Polymorphonuclear neutrophils (PMNs) are normally the most numerous of the circulating leucocytes (40-75%). The cytoplasm of PMNs contains lysosomal granules of three types: 1- Primary ( Azurophilic ) 2- Secondary 3- Tertiary.

29. Primary granules ( azurophilic ): - contain myeloperoxidase which creates anti-bacterial compounds, acid hydrolases and defensins . Secondary granules (specific): are the most numerous type: - contain complement activators and enzymes e.g. collagenases . Tertiary granules: Either phosphatases or metalloproteinases with the later aiding movement through connective tissue.

30. PMNs have similar function to those of macrophages and are therefore appropriately referred to as ‘ microphages’ owing to their role as first line of defense against an invading foreign organism in the body. However, these cells have limitation of size and type of organisms to be engulfed E.g. while they are capable of acting against bacteria and small foreign particulate material but not against viruses and large particles.

31. Basophils and Mast Cells Basophils are a type of circulating granulocytes (0-1%) while mast cells are their counterparts seen in tissues, especially in connective tissue around blood vessels and in sub mucosal location. Basophils and mast cells have IgE surface receptor; thus on coming in contact with antigen binding to IgE (e.g. allergic reaction to parasites), these cells get activated and release granules i.e. they degranulate.

32. These granules contain active substances such as histamine, platelet activating factor, heparin and certain chemical mediators (e.g. prostaglandins, leukotrienes).

33. Eosinophils Eosinophils are also circulating granulocytes (1-6%). These cells play a role in allergic reactions and in intestinal helminthiasis. The granules of eosinophils contain lysosomal enzymes, peroxidases, and chemical mediators of inflammation (e.g. prostaglandins, leukotrienes). On coming in contact with IgE opsonised antigen (e.g.helminths), eosinophils degranulate and release the chemicals stored in granules and incite inflammation.

34. Lymphocytes Lymphocyte is the master of human immune system. Two major lymphocyte populations: - T and B lymphocytes Third type: - NK (natural killer) cells (small percentage of circulating lymphocytes having the distinct appearance of large granular lymphocytes)

35. Formed from lymphoid precursor cells in the bone marrow.

36. B- Lymphocytes undergo maturation and differentiation in the bone marrow. T cells undergo maturation and differentiation in the Thymus. During this process: - They acquire certain genetic and immune surface characters which determine their type and function. i.e., Cluster of differentiation (CD) molecules on their surface.

37. B cells differentiate into plasma cells which form specific antibodies. T cells get functionally activated on coming in contact with appropriate antigen. The Major Histocompatibility complex on antigen presenting cell (eg: Macrophage) determine whether the invading antigen is to be presented to B-Cell or T-Cell.

38. Features and functions of subtypes of lymphocytes B CELLS: They function in the humoral immunity component of the adaptive immune system by secreting antibodies. The undifferentiated B cells present surface antibodies like IgM and IgD also known as B-cell receptors (BCR) or surface antibodies.  And the differentiated B cell i.e.,  plasma cells secrete free antibodies into blood plasma,

39. FREE ANTIBODIES IN THE BLOOD PLASMA, ANTIBODIES ATTACHED TO B-CELL SURFACE

40. Depending upon the maturation stage of B cells, specific CD molecules appear on the cell surface which can be identified by CD markers. Common B cell markers are: - CD 45, 19, 20, 21, 22, 23.

41. T CELLS Implicated in inciting cell-mediated immunity. They are higher in number compared to B-cells. Common T cell markers are CD45, CD3 Depending upon functional activity, T cells have two major subtypes: T-helper (or CD4+) cells. T suppressor (or CD8+) cells.

42. T helper cells Abbreviated as T H cells, these cells promote and enhance the immune reaction and are also termed as T-regulatory cells. They carry special CD4 molecule along with CD45, CD3 on their surface and hence are also called CD4+ cells. CD4+ cells in circulation are about twice the number of CD8+ cells (CD4+/CD8 ratio 2:1).

43. These cells act by production of variety of cytokines (EX: INTERLEUKINS) Depending upon the type of cytokines produced, these T H cells are further of two subclasses: 1- T H 1 2- T H 2. T H 1 cells produce- IL-2 and interferon (IFN)- γ . T H 2 cells produce- IL-4, IL-5, IL-6, and IL-10.

44. CD4+ cells are predominantly involved in cell-mediated reactions to: Viral infections (e.g. In HIV), Tissue transplant reactions Tumour lysis .

45. T suppressor cells Abbreviated as TS cells, they suppress immune reactions but are cytotoxic and actually destroy the invading antigen; hence are also termed as cytotoxic T lymphocytes (CTL) /Killer T cell. These cells carry special CD8 molecule along with CD45, CD3 molecules on their surface and hence are also called CD8+ cells. CD8+ cells in circulation are about half the number of CD4+ cells..

46. Compared to CD4+ cells which act by releasing of cytokines, CD8+ cells are directly cytotoxic to the antigen.

47. CD8+ cells are particularly involved in Destroying cells infected with viruses, Foreign cells and Tumour cells.

48. NATURAL KILLER (NK) CELLS They are the circulating large granular lymphocytes. These lymphocytes do not have B or T cell markers (CD45), nor are these cells dependent upon thymus for development unlike CD4+ and CD8+ T cells. NK cells carry surface molecules of CD2, CD16 and CD56, but negative for T cell marker CD3.

49. NK cells are part of the natural or innate immunity. These cells recognize antibody-coated target cells and bring about killing of the target directly. This process is termed as Antibody-dependent Cell-mediated Cytotoxicity (ADCC)

50. ANTIGEN PRESENTING CELL An  antigen-presenting cell  ( APC ) or  accessory cell  is a cell that displays antigen complexed with major histocompatibility complexes (MHCs) on their surfaces; this process is known as antigen presentation.  Examples:   1- Dendritic cells 2- Macrophages 3- B cells

51. Almost all cell types can serve as some form of APC. They are found in a variety of tissue types. Professional antigen-presenting cells, including macrophages, B cells and dendritic cells, present foreign antigens to helper T cells, while other cell types can present antigens originating inside the cell to cytotoxic T cells.

52. Antigen-presenting cells are vital for effective  adaptive immune response , as the functioning of both cytotoxic and helper T cells is dependent on APCs. T cells cannot recognize and respond to, 'free' or soluble antigens.  T cells may recognize these complexes using their T cell receptors (TCRs). These cells process antigens and present them to T-cells.

53. They can only recognize and respond to antigen that has been processed and presented by cells via carrier molecules like MHC molecules. Those that express MHC class II molecules are called  professional antigen-presenting cells . The non-professional APCs express MHC class I molecules

54. Antigen-presenting cells fall into two categories: 1- Professional 2- Non-professional

55. Professional APC Professional APCs specialize in presenting antigen to T helper cells.  They are very efficient at internalizing antigens- either by  Phagocytosis (macrophages and dendritic cells) or Receptor-mediated endocytosis (B cells) After processing the antigen into peptide fragments and then displaying those peptides, bound to a class II MHC molecule, on their membrane.

56. Phagocytosis (macrophages)

57. Receptor-mediated endocytosis (B-CELL) 

58. The T cell recognizes and interacts with the antigen-class II MHC molecule complex on the membrane of the antigen-presenting cell. An additional co-stimulatory signal is then produced by the antigen-presenting cell, leading to activation of the T cell. The main types of professional antigen-presenting cells are Dendritic cells, Macrophages and B cells

59. Antibodies production by B-cells Antibodies production by B-cells takes by following ways: 1- T-Helper cell independent B-Cell Activation 2- T- Helper cell dependent B-Cell Activation by interleukins (IL-4, IL-5, IL-10, IL-13).

60. T-Helper cell independent B-Cell Activation Bacterial polysaccharides and lipopolysaccharides , and some polymeric proteins, can stimulate B lymphocytes without involvement of T-Helper cells.

61. Y Y Y Y POLYSACCHARIDE ANTIGENS Y Y Y Y Y Y Y ANTIBODIES PLASMA CELLS Y Clonal expansion Differentiation

62. T-Helper cell dependent B-Cell Activation by interleukins (IL-4, IL-5, IL-10, IL-13). For most protein antigens, the production of antibodies by B lymphocytes is dependent on stimulation of T-Helper cells.

63. MHC CLASS 2 MOLECULE COMPLEXED WITH ANTIGEN MACROPHAGE BACTERIA RECEPTOR LYSOSOMES PHAGOSOME

64. T-HELPER CELL I L-1 helps in maturing the T-Helper cell to T-H1 cell Receptor (IL-1R) for IL-1 B7 MOLECULE CD28 T-CELL RECEPTOR

65. IL-2 IL-2 R CLONAL T-HELPER CELLS MITOSIS (CLONAL EXPANSION) ACTIVATED T-H1 CELL

66. Y Y CD79 PROTEIN ANTIGEN B-LYMPHOCYTE MHC II-ANTIGEN COMPLEX

67. CLONAL T-HELPER CELLS RELEASE IL-4 FOR B-CELL MULTIPLICATION RELEASE IL-5 FOR B-CELL DIFFERENTIATION IL-4 B-CELL MULTIPLICATION ACTIVATED CLONAL T-HELPER CELLS IL-5 B-CELL DIFFERENTIATION Y Y Y Y Y CD40L CD40 TCR-MHC II-PEPTIDE COMPLEX

68. Now activated, B cells participate in a two-step differentiation process that yields both Short-lived plasmablasts for immediate protection ( plasmablasts produce early, weak antibodies mostly of class IgM ) Long-lived plasma cells and memory B cells for persistent protection (Strong antibodies)

69. Autoimmune disease can result from abnormal B cell recognition of self-antigens followed by the production of autoantibodies. Autoimmune diseases where disease activity is correlated with B cell activity include Scleroderma, Multiple Sclerosis, Systemic Lupus Erythematosus, Type 1 Diabetes, and Rheumatoid Arthritis

70. CYTOKINES Cytokine: Any low-molecular-weight regulatory protein or glycoprotein secreted by immune cells or other cells of the body in response to an stimuli. Cytokines through interaction with specific cell surface receptors, regulate the development or function of another cell. Cytokines are proteins with specific roles in communication between cells of the immune system.

71. Presently, about 200 cytokines have been identified. Many cytokines are referred to as “interleukins” because they are secreted by some leukocytes and act on other leukocytes.

72. MODE OF ACTION OF CYTOKINES Cytokines may act in one of the following 3 ways: 1) Autocrine when a cytokine acts on the cell which produced it. 2) Paracrine when it acts on another target cell in the vicinity. 3) Endocrine when the cytokine secreted in circulation acts on a distant target.

73. AUTOCRINE ACTION

74. PARACRINE ACTION

75. ENDOCRINE ACTION

76. Cytokine Properties. 1. Cytokines can be Pleiotropic:

77. 2. Cytokines can be Redundant

78. 3. Cytokines can be Synergistic

79. 4. Cytokines can be Antagonistic

80. 5. Cytokine Cascade Induction Certain cytokines induce a pyramid of effects, including a cascade of cytokine secretion. The action of one cytokine on a target cell induces that cell to produce one or more cytokines. This, in turn, may induce other target cells to produce other cytokines.

81. TYPES OF CYTOKINES INTERLEUKINS: (IL-1 to IL-38) INTERFERONS: (INF- α , INF- β , INF- γ ) TUMOUR NECROSIS FACTORS: (TNF- α , TNF- β ) TUMOUR GROWTH FACTORS: (TGF- β 1) COLONY STIMULATING FACTORS: MONOCYTE-COLONY STIMULATING FACTOR (M-CSF) GRANULOCYTE- COLONY STIMULATING FACTOR (G-CSF) GRANULOCYTE-MACROPHAGE STIMULATING FACTOR (GM-CSF)

82. INTERLEUKIN-1 IL-1 is intensely produced by tissue macrophages, monocytes, fibroblasts, and dendritic cells, but is also expressed by B lymphocytes, NK cells, microglia, and epithelial cells. They form an important part of the inflammatory response of the body against infection. These cytokines increase the expression of adhesion factors on endothelial cells to enable transmigration (also called diapedesis) of immunocompetent cells, such as phagocytes, lymphocytes and others, to sites of infection.

83. They also affect the activity of the hypothalamus, the thermoregulatory center, which leads to a rise in body temperature (fever) . That is why IL-1 is called an endogenous pyrogen. Besides fever, IL-1 also causes hyperalgesia (increased pain sensitivity), vasodilation and hypotension.

84. CLASSIFICATION: Cytokine Families Hematopoietin family. Interferon (IFN) family. Chemokine family. Tumor Necrosis Factor (TNF) family.

85. 1. Hematopoietin family. Cytokines  of the  hematopoietic  system include Interleukins (ILs) ( IL-2, IL-3, IL-4, IL-5, IL-6, IL-6, IL-7, IL-9.) Colony-Stimulating Factors (CSFs), Erythropoietin (EPO) and Thrombopoietin (TPO)

86. Cytokine Function in hematopoiesis Erythropoietin (EPO) Red blood cell production Granulocyte-macrophage colony stimulating factor (GM-CSF) Stimulation of diverse set of granulocyte-macrophage colonies Granulocyte-colony stimulating factor (G-CSF) granulocytic colony stimulation Interleukin-2 (IL-2) T-cell proliferation Interleukin-3 (IL-3) Granulocyte , macrophage, eosinophil , megakaryocyte and erythroid colony formation Interleukin-5 (IL-5) B-cell differentiation and eosinophil regulation Interleukin-6 (IL-6) B-cell differentiation Interleukin-7 (IL-7) T-lymphocyte induction Interleukin-11 (IL-11) Stimulation of megakaryocytes and plasmacytoma cell lines Leukemia inhibitory factor (LIF) Differentiation and suppression of clonogenicity of leukemic cells Macrophage-colony stimulating factor (M-CSF) Macrophage colony stimulation Stem cell factor (SCF) Proliferation of mast cells and stem cells Thrombopoietin (TPO) Regulation of platelet production; stimulation of megakaryocytes with IL-3 and SCF

87. 2. INTERFERONS FAMILY. IFNs are class of proteins known as cytokines, molecules used for communication between cells to trigger the protective defenses of the immune system that help eradicate pathogens especially viruses. Certain symptoms of infections, such as fever, muscle pain and "flu-like symptoms", are also caused by the production of IFNs and other cytokines.

88. They are typically divided among three classes: Type I IFN, Type II IFN, and Type III IFN. IFNs belonging to all three classes are important for fighting viral infections and for the regulation of the immune system.

89. 3. CHEMOKINES ( Chemotactic cytokines) Chemokines are small protein molecules that are produced by the cells of the immune system. These act as chemo-attractants, leading to the migration of immune cells to an infection site so they can target and destroy invading bodies such as microbes. Eg:  The chemokines that attract Macrophages to the site of inflammation are CCL2, CCL3

90. Chemokines have been classified into four main subfamilies: CXC, CC, CX3C XC

91. 4. TUMOR NECROSIS FACTOR FAMILY : Also called cachexin , or  cachectin Produced chiefly by activated macrophages, although it can be produced by many other cell types such as CD4+ Lymphocytes, NK Cells, Neutrophils, Mast Cells, Eosinophils. TNF is able to induce fever, apoptotic cell death, cachexia, inflammation and to inhibit tumorigenesis and viral replication.

92. TNF is an important endogenous pyrogen, together with IL-1, it is responsible for many of the hematological changes in septic shock. A local increase in concentration of TNF will cause the cardinal signs of Inflammation to occur: Heat, Swelling, Redness, Pain, Loss of function.

93. Whereas high concentrations of TNF induce shock-like symptoms. The prolonged exposure to low concentrations of TNF can result in cachexia , a wasting syndrome. This can be found, for example, in cancer patients.

94. HLA SYSTEM AND MAJOR HISTOCOMPATIBILITY COMPLEX HLA stands for Human Leucocyte Antigens because these are antigens or genetic proteins in the body that determine one’s own tissue from non-self (histocompatibility) (The HLA complex helps the immune system distinguish the body's own proteins from proteins made by foreign invaders such as viruses and bacteria.) First discovered on the surface of leucocytes.

95. Subsequently, it was found that HLA are actually gene complexes of proteins on the surface of all nucleated cells of the body and platelets. Since these complexes are of immense importance in matching donor and recipient for organ transplant, they are called Major Histocompatibility Complex (MHC) or HLA complex.

96. In humans, the MHC complex consists of more than 200 genes located close together on  chromosome 6 . Genes in this complex are categorized into three basic groups: CLASS I CLASS II CLASS III

97. 1) MHC class I genes: HLA-A  HLA-B HLA-C 2) MHC class II genes: HLA-DP α 1 HLA-DP β 1 HLA-DQ α 1  HLA-DQ β 1  HLA-DR α 1 HLA-DR β 1 HLA-DR β 2

98. Some histocompatibility complex genes have hundreds of identified versions (alleles), each of which is given a particular number. Example: HLA-B GENE has other variants/alleles such as HLA-B27. The variants/alleles has further subtypes- HLA-B2701, HLA-B2702, HLA-B2703.

99. Class I MHC antigens MHC class I genes: HLA-A  HLA-B HLA-C The proteins produced from these genes are present on the surface of almost all cells. On the cell surface, these proteins are bound to protein fragments (peptides) that have been exported from within the cell. MHC class I proteins display these peptides to the immune system.

100. If the immune system recognizes the peptides as foreign (such as viral or bacterial peptides), it responds by triggering the infected cell to self-destruct. CD8+ (i.e. T suppressor) lymphocytes carry receptors for class I MHC; these cells are used to identify class I antigen on them.

101. CD8+ T CELL TCR ANTIGEN MHC-1 TUMOUR CELL

102. Class II MHC antigens MHC class II genes provide instructions for making proteins that are present almost exclusively on the surface of certain immune system cells. Like MHC class I proteins, these proteins display peptides to the immune system. Class II MHC is identified by B cells and CD4+ (i.e. T helper) cells.

103. CD4+ T CELL TCR ANTIGEN MHC-2 MACROPHAGE

104. Class III MHC antigens Class III MHC antigens are some components of the complement system (C2 and C4) coded on HLA complex but are not associated with HLA expression and are not used in antigen identification.

105. PATHOLOGY OF HLA GENES More than 100 diseases have been associated with different alleles of histocompatibility complex genes. For example, the HLA-B27 allele increases the risk of developing an inflammatory joint disease called ankylosing spondylitis. Many other disorders involving abnormal immune function and some forms of cancer have also been associated with specific HLA alleles. However, it is often unclear what role histocompatibility complex genes play in the risk of developing these diseases.