IMMUNE SYSTEM

The immune system

• What is the main function of the immune system?

• What is a pathogen?

The defense mechanisms

• 1st line vs 2nd line vs 3rd line of defenses

Give the function of these cells

• Monocytes APC coelomocytes

• Macrophages Basophil

• Neutrophil Eosinophil

• Mast cell NK cell

• Cytokine cytotoxic T cell

• effector cell helper T cell

• memory cell suppressor T cell

• T cell B cell

• Lymphocyte granulocyte

• Plasma cell memory cell

The chemicals and others

• Perforin Chemokine

• Interferon antibody

• Antigen antigen receptor

• Cd4 Cd8

• Histamine Interleukin

• Lysozyme prostaglandins

• Pyrogens Rh factor

• MHC genes hemolin

The innate immunity

• What happens to you if you caught a virus or an infection?

Inflammation and Sepsis

• Release of histamines (pathogen/self cell)

• Dilation and inc permeability of BV (prostaglandin)

• Increased blood flow

• Inflammation (redness and swelling)

Phagocytic cells

• Neutrophils are first to arrive

• Macrophages will also arrive

Chemokines

• Messenger chemical

• Attracts phagocytic cells

• Activation of lysozyme action

Severe infection

• Fever is an immune response to severe infection– Can be caused by the pathogens

– May be due to pyrogens released by some leukocytes

– Can facilitate phagocytosis

Septic shock- high fever, hypotension

Antimicrobial proteins

• Proteins that attack microbes or stall reproduction of microbes

• Lysozyme is an example

• Also, presence of the complement system– Made up of 20 serum proteins

– Action: lysis or attraction of phagocytic cells

– Is also part of specific immune response

Interferons

– Secreted by virus-infected cells

– Neighboring cells are stimulated to produce chemicals that can inhibit viral infection

– Not virus-specific

– A specific type of interferon activates phagocytes

Self vs Non-self

• Have you asked yourselves the question who am I?

Self vs Non-self

• Lymphocytes react on special surface glycoproteins encoded by genes called Major Histocompatibilty Complex (MHC)

• In Humans, Human Leukocyte Antigens (HLA)

• Class I MHC- Almost all nucleated cells

• Class II MHC- macrophages, B cells, activated T cells, cell in the interior of the thymus

Varies from one person to another

Specific immunity: the third line of defense

• Lymphocytes- cells responsible for the specific immune response

• There are two types: B cells and T cells (NK cells another type)

• Antigen- molecules that elicit specific response from lymphocyte– E.g. Molecules from bacteria, fungi, virus, parasitic

worms

• Antigens activate B cell in producing antibodies

Recognition of antigens by B cells and T cells

• Specificity is possible because of membrane-bound antigen receptor

• B cell antigen receptor- transmembrane version of antibodies– Also called membrane antibodies

• T cell antigen receptor- called T cell receptor– Structurally related to membrane antibodies

– T cell receptor never released in secreted form

Clonal selection

Clonal selection

• Antigen binds to a specific antigen receptor (B cell)

• B cell produces its clone

• Some B cells become plasma cells (short-lived) that can secrete antibodies to the specific antigen– Plasma cells- also called effector cells

• Some B cells become memory cells (long-lived) for re-exposure to the antigen

Immunological memory

• Primary immune response- selective proliferation and differentiation of lymphocytes upon first exposure– 10-17 days to develop maximum effector cells

– Selected B cells and T cells produce their respective effector cells

Immunological memory

• Secondary immune response- re-exposure to the same antigen– response is faster, greater magnitude, more

prolonged

– Also, more antibodies are produced

– Antibodies have greater affinity to the antigens

– Secondary response is called immunological memory

Graph showing immunological memory

Lymphocyte development

• All blood cells develop from pluripotent cells

• Lymphocytes also develop from pluripotent cells

• T cells- mature in the thymus

• B cells- mature in the bone marrow

Immune tolerance for self

• Maturing lymphocytes’ antigen receptors are rendered non-functional

• If antigen receptors cannot be switched off, lymphocytes undergo apoptosis

The other cells....

• Cytotoxic T cells- kill cells through lysis

• Helper T cells- bind to antigen cell and secretes cytokine

• Antigen-presenting cells (APCs)- engulf bacteria (virus) and present fragment of these pathogens to other lymphocytes

Humoral response and cell-mediated response

• Humoral immunity- involves B cell activation, production of antibodies in blood plasma and lymph called humor

• Cell-mediated immunity- action of T cells

Overview of humoral response

• Macrophage engulfs the pathogen

• Class II MHC binds to fragment of pathogen

• MHC-antigen complex is presented by the phagocytic cell

• A helper T cell with specific receptor for the antigen makes contact with the macrophage and releases cytokines

Overview of humoral response

• Activated T cell presents the antigen to a B cell

• Cytokines activates the B cell

• Activated B cells differentiate into plasma and memory cells

• Plasma cells will produce the specific antibodies

Cell-mediated immune response

• Occurs when antigen displayed by APC activates Cytotoxic T cell

• Cytotoxic cell can differentiate to Memory T cells or active cytotoxic T cells

• Active against cancer cells and pathogens

• Kills these cell through lysis

Antibodies

• Do not destroy antigens directly

• Rather, neutralizes it or present it as a target for opsonization, agglutination, precipitation, or complement fixation, neutralization

Antibodies

• Opsonization- coating of antigens by antibodies to facilitate phagocytos

• Neutralization- binds to the antigen and inactivates it

• Agglutination- clumping of bacteria or virus to effectively neutralize or opsonize it

• Complement fixation or precipitation- immune adherence occurs– Microbes coated with antibodies and complement

proteins adhere to BV walls

The ABO blood type

• A and B are the antigens

• Type A has antigen A and antibody B

• Type B has antigen B and antibody A

• Type AB has both antigen but no antibody

• Type O has no antigen but has both antibody IgM not IgG

Rh Factor IgG can cross the placenta ++ = + +- = + - - = -

Passive vs Active Passive

short-lived

Active Natural vs artificial

Immunodeficiency vs Autoimmune disease