Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to...

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Government Science College, Gandhinagar Dr Arefa Baakza Department of Microbiology Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The Immune system deals with: A less specific Innate Immunity A more specific Adaptive Immunity Overview of the Immune System Immune System Innate (Nonspecific) 1 o line of defense Adaptive (Specific) 2 o line of defense Protects/re - exposure Cellular Components Humoral Components Cellular Components Humoral Components Interactions between the two systems Innate immunity is the immunity that is immediately available without having to adapt to the specific pathogen that is present. It is an inborne immunity. It is not specific to a particular organism such that identical responses can protect against several organisms. Innate immunity is mediated by phagocytes (cell that ingest bacteria or other particulate matter) such as macrophages and neutrophils. It is also mediated by chemical compounds and physical barriers. Adaptive Immunity: Specific Immune Response (e.g., antibody) against a particular microorganism is an adaptive immune response. That is, it occurs during one’s lifetime as an adaptation to the presence of that particular organism. (usually, the term specific means the ability to distinguish one organism from another)

Transcript of Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to...

Page 1: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

Basic Concepts In Immunology

Immunity means Nonsusceptibility to disease.

It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’

The Immune system deals with: A less specific Innate Immunity A more specific Adaptive Immunity

Overview of the Immune System

Immune System

Innate(Nonspecific)

1o line of defense

Adaptive(Specific)

2o line of defenseProtects/re-exposure

Cellular Components Humoral Components Cellular Components Humoral Components

Interactions between the two systems

Innate immunity is the immunity that is immediately available without having to adapt to the specific pathogen that is present. It is an inborne immunity. It is not specific to a particular organism such that identical responses can protect against several organisms.

Innate immunity is mediated by phagocytes (cell that ingest bacteria or other particulate matter) such as macrophages and neutrophils. It is also mediated by chemical compounds and physical barriers.

Adaptive Immunity:Specific Immune Response (e.g., antibody) against a particular microorganism is an adaptive immune response. That is, it occurs during one’s lifetime as an adaptation to the presence of that particular organism. (usually, the term specific means the ability to distinguish one organism from another)

Page 2: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

Adaptive immune response is Specific, shows diversity, can differentiate between self and non-self, has an immunological memmry.

Adaptive immunity involves the participation of Lymphocytes, APCs and MHCs.

Together, innate and adaptive immunity prevent most infectious diseases (no symptoms from exposure to the microorganisms) or cure infections

Comparison of Innate and Adaptive Immunity

Innate Immunity Adaptive Immunity

No time lag A lag period

Not antigen specific Antigen specific

No memory Developmentof memory

Page 3: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

Innate Host Defenses Against Infection

• Anatomical barriers– Mechanical factors– Chemical factors– Biological factors

• Humoral components– Complement– Coagulation system– Cytokines

• Cellular components– Neutrophils– Monocytes and macrophages– NK cells– Eosinophils

Anatomical Barriers - Mechanical Factors

System or Organ Cell type Mechanism

Skin Squamous epithelium Physical barrierDesquamation

Mucous Membranes

Non-ciliated epithelium(e.g.GI tract)

Peristalsis

  Ciliated epithelium (e.g. respiratory tract)

Mucociliary elevator

  Epithelium (e.g. nasopharynx)

Flushing action of tears, saliva, mucus, urine

Anatomical Barriers - Chemical Factors

System or Organ Component Mechanism

Skin Sweat Anti-microbial fatty acids

Mucous Membranes

HCl (parietal cells)Tears and saliva

Low pHLysozyme and phospholipase A

  Defensins (respiratory & GI tract)

Antimicrobial

  Sufactants (lung) Opsonin

Page 4: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

Anatomical Barriers - Biological Factors

System or Organ Component Mechanism

Skin and mucous membranes

Normal flora Antimicrobial substancesCompetition for nutrients and colonization

Humoral Components

Component Mechanism

Complement Lysis of bacteria and some virusesOpsoninIncrease in vascular permeabilityRecruitment and activation of phagocytic cells

Coagulation system

Increase vascular permeabilityRecruitment of phagocytic cellsΒ-lysin from platelets – a cationic detergent

Lactoferrin and transferrin

Compete with bacteria for iron

Lysozyme Breaks down bacterial cell walls

Cytokines Various effects

Cellular Components

Cell Functions

Neutrophils Phagocytosis and intracellular killingInflammation and tissue damage

Macrophages Phagocytosis and intracellular killingExtracellular killing of infected or altered self targetsTissue repairAntigen presentation for specific immune response

NK and LAK cells

Killing of virus-infected and altered self targets

Eosinophils Killing of certain parasites

Page 5: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

ORIGIN OF CELLS OF IMMUNE SYSTEM

Page 6: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

Page 7: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

The Adaptive Immune System Requires Cooperation Between Lymphocytes and Antigen-Presenting Cells

1) An effective immune response involves two major groups of cells: T lymphocytes and antigen-presenting cells. Lymphocytes are one of many types of white blood cells produced in the bone marrow by the process of hematopoiesis.

2) Lymphocytes leave the bone marrow, circulate in the blood and lymphatic systems, and reside in various lymphoid organs. Because they produce and display antigenbinding cell-surface receptors, lymphocytes mediate the defining immunologic attributes of specificity, diversity, memory, and self/nonself recognition. The two major populations of lymphocytes are —B lymphocytes (B cells) and T lymphocytes (T cells)

B lymphocytes mature within the bone marrow; when they leave it, each expresses a unique antigen-binding receptor on its membrane. This antigen-binding or B-cell receptor is a membrane-bound antibody molecule.

Page 8: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

Antibodies are glycoproteins that consist of two identical heavy polypeptide chains and two identical light polypeptide chains. Each heavy chain is joined with a light chain by disulfide bonds, and additional disulfide bonds hold the two pairs together. The amino-terminal ends of the pairs of heavy and light chains form a cleft within which antigen binds.When a naive B cell (one that has not previously encountered antigen) first encounters the antigen that matches its membranebound antibody, the binding of the antigen to the antibody causes the cell to divide rapidly; its progeny differentiate into memory B cells and effector B cells called plasma cells. Memory B cells have a longer life span than naive cells, and they express the same membrane-bound antibody as their parent B cell. Plasma cells produce the antibody in a form that can be secreted and have little or no membrane-bound antibody. Although plasma cells live for only a few days, they secrete enormous amounts of antibody during this time. It has been estimated that a single plasma cell can secrete more than 2000 molecules of antibody per second. Secreted antibodies are the major effector molecules of humoral immunity.

T LYMPHOCYTES

T lymphocytes also arise in the bone marrow. Unlike B cells, which mature within the bone marrow, T cells migrate to the thymus gland to mature. During its maturation within the thymus, the T cell comes to express a unique antigen-binding molecule, called the T-cell receptor, on its membrane.Unlike membrane-bound antibodies on B cells,which can recognize antigen alone, T-cell receptors can recognize only antigen that is bound to cell-membrane proteins called major histocompatibility complex (MHC) molecules. MHC molecules function in an event, which is termed “antigen presentation,” are glycoproteins found on cell membranes. There are two major types of MHC molecules: Class I MHC molecules, which are expressed by nearly all nucleated cells of vertebrate

Page 9: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

species. Class II MHC molecules, which consist of an alpha and a beta glycoprotein chain, are expressed only by antigen-presenting cells.

When a naive T cell encounters antigen combined with a MHC molecule on a cell, the T cell proliferates and differentiates into memory T cells and various effector T cells. There are two well-defined subpopulations of T cells: T helper (TH) and T cytotoxic (TC) cells.T helper and T cytotoxic cells can be distinguished from one another by the presence of either CD4 or CD8 membrane glycoproteins on their surfaces .

T cells displaying CD4 generally function as TH cells, whereas those displaying CD8 generally function as TC cells.

After a TH cell recognizes and interacts with an antigen– MHC class II molecule complex, the cell is activated—it becomes an effector cell that secretes various growth factors known collectively as cytokines.

The secreted cytokines play an important role in activating B cells, TC cells, macrophages, and various other cells that participate in the immune response.

Under the influence of TH-derived cytokines, a TC cell that recognizes an antigen–MHC class I molecule complex proliferates and differentiates into an

Page 10: Basic Concepts In Immunology · Basic Concepts In Immunology Immunity means Nonsusceptibility to disease. It comes from the Latin word ‘immunis’ meaning ‘to Exempt from’ The

Government Science College, Gandhinagar

Dr Arefa BaakzaDepartment of Microbiology

effector cell called a cytotoxic T lymphocyte (CTL). In contrast to the TC cell, the CTL generally does not secrete many cytokines and instead exhibits cell-killing or cytotoxic activity. The CTL has a vital function in monitoring the cells of the body and eliminating any that display antigen, such as virus-infected cells, tumor cells, and cells of a foreign tissue graft.