Unit Six: Blood Cells, Immunity, and Blood

Coagulation

Chapter 34: Resistance of the Body to Infection. II. Immunity and Allergy Innate

Immunity

Guyton and Hall, Textbook of Medical Physiology, 12th edition

Innate Immunity

• Innate Immunity

a. Phagocytosis of bacteria and other invaders by wbcs andcells of the tissue macrophage system

b. Destruction of swallowed organisms by stomachacid and digestive enzymes

c. Resistance of the skin to invasion

d. Presence of antibacterial chemicals (i.e. lysozyme,complement, NK cells, etc.)

Acquired (Adaptive) Immunity

• Basic Types

a. Humoral or B-cell Immunity

b. Cell-mediated or T-cell immunity

• Initiation of the Responses- antigens

a. MW greater than 8000

b. Epitopes or antigenic determinants on surface

c. Generally protein or large polysaccharides

Lymphocytes

• T and B Lymphocytes

a. T lymphocytes migrate from the bone marrow to thethymus where they mature and are responsible forcell mediated immunity

b. B lymphocytes are preprocessed in the liver, then the bonemarrow and are responsible for antibody productionThe “B” designation originated from the bursa of Fabricius in the chicken.

Fig. 34.1 Formation of antibodies and sensitized lymphocytes from a lymph node in response to antigens

Lymphocytes (cont.)

• Preprocessing of the T Lymphocytes-occurs shortly before or just after birth

a. In the thymus each T cell develops specificity againstone antigen

b. Continues until there are thousands of different T cellswith specific reactivities against 1000s of antigens

c. T cells then migrate to the secondary lymphoid tissues

d. T cells capable of reacting against “self-antigens” aredestroyed instead of being released

Lymphocytes (cont.)

• Preprocessing of the Lymphocytes

a. Instead of the whole cell developing reactivity againstthe antigen, the B cells actively secrete antibodies thatare the reactive agents

b. Greater diversity than T cells: can form millions of types of antibodies with different specific reactivities

• T-Cells and B-Cell Antibodies React Highly SpecificallyAgainst Specific Antigens-Role of Lymphocyte Clones

Lymphocyte Clones

Fig. 34.2

Lymphocyte Clones (cont.)

a. Millions of specific types of lymphocytes are stored inthe lymphoid tissues

b. Origin of the many clones of lymphocytes

c. Mechanism for activating a clone of lymphocytes

d. Role of macrophages

e. Role of the T cell in the activation of B cells

Humoral Immunity and the Antibodies

• Formation of Antibodies by Plasma Cells

• Formation of “Memory” Cells

• Difference Between Primary and Secondary Responses

Humoral Immunity and the Antibodies

Fig. 34.3 Primary and secondary antibody responses

Antibodies (cont.)

• Nature of Antibodies

a. Gamma globulins (immunoglobulins

b. MW between 170,000 and 970,000

c. Make up 20% of all the plasma proteins

d. Consist of heavy and light polypeptide chains

e. Have variable and constant regions

Antibodies (cont.)

Fig. 34.4 Structure of the typical IgG antibody

Antibodies (cont.)

• Specificity of Antibodies-each antibody is specificfor a particular antigen

Ka is the affinity constant and a measure ofhow tightly the antibody binds to the antigen

Antibodies (cont.)

• Classes of Antibodies

Class Structure

Location

MW Half-LifeIn

Serum

Function

IgG Monomer Blood, Lymph,

Intestine170,000 23 days

Phagocytosis, neutralization, crosses placenta

IgM Pentamer Blood, Lymph, B

cell surface

970,000 5 daysPrimary

response, phagocytosi

s, agglutinatio

n

IgA Dimer Secretions

405,000 6 days Mucosal ab

IgD Monomer B cell surface

175,000 3 days Surface Ig on B cells

IgE Monomer Cell bound to

mast cells and basophils

190,000 2 days Allergic Reactions,pa

rasitic reactions

Antibodies (cont.)

• Mechanism of Action of Antibodies (Direct)

a. Agglutination

b. Precipitation

c. Neutralization

d. Lysis

Antibodies (cont.)

• Mechanism of Action of Antibodies (Indirect)-the

Complement System

Fig. 34.6

Antibodies (cont.)

• Classic Pathway

a. Opsonization and phagocytosis

b. Lysis

c. Agglutination

d. Neutralization of viruses

e. Chemostaxis

f. Activation of mast cells and basophils

g. Inflammatory effects

Activated T Cells and Cell-Mediated Immunity

• Release of Activated T Cells From Lymphoid Tissueand Formation of Memory Cells

• APCs, MHC Proteins, and Antigen Receptors onT lymphocytes

Activated T Cells and CMI (cont.)

Fig. 34.7 Activation of T cells requires interaction of T cell receptors with an antigen that is transported to the surface of the APC by a MHC protein.

Types of T Cells

• Helper T Cells—Role in Overall Regulation of Immunity

a. Production of lymphokines (i.e. interleukins 2,3,4,5,6 and gamma interferon)

b. Specific regulatory functions of the lymphokines

c. Stimulation of growth and proliferation of cytotoxic T cells and suppressor T cells

d. Stimulation of B cell growth and differentiation to form plasma cells and antibodies

Types of T Cells (cont.)

• Helper T Cells—Role in Overall Regulation of Immunity (cont.)

e. Activation of the macrophage system

f. Feedback stimulatory effect on the helper

cells themselves

Types of T Cells (cont.)

Fig. 34.8 Regulation of the immune system

Types of T Cells (cont.)

• Cytotoxic T Cells are “Killer” Cells

Fig. 34.9 Direct destruction of an invading cell by sensitize T cytotoxic cells

Types of T Cells (cont.)

• Suppressor T Cells

a. Can suppress the functions of both T helper and T cytotoxic cells

b. Regulatory cells—prevent excessive immune reactions that might be damaging to the host

Tolerance

• Tolerance to One’s Own Tissues

• Results from Clone Selection During Preprocessing

• Failure Leads to Autoimmune Diseases

a. Rheumatic feverb. Glomerulonephritisc. Myasthenia gravisd. Systemic lupus erythematosus (SLE)

Immunization

• Active Immunity

a. Artificially acquiredb. Naturally acquired

• Passive Immunity

a. Artificially acquiredb. Naturally acquired

Allergy and Hypersensitivity

• Type I Hypersensitivity (IgE antibody mediated)

a. Anaphylaxis b. Urticariac. Hay feverd. Mast cell involvement and histamine

• Type II Hypersensitivity (Cytotoxic reactions)

• Type III Hypersensitivity (Immune complex)

• Type IV Hypersensitivity (Delayed cell mediated)