Human Anatomy and Physiology

Immunology: Adaptive defenses

Overview

System must be primed before it can take effect

1800 experiment Inject a bacteria into an animal It raises proteins (antibodies against the

infection Serum containing antibodies protects other

animals not previously exposed

Overview

Characteristics of adaptive response Specific recognition of pathogens Response is systemic Response has memory (mounts a stronger

attack on subsequent exposure) Injecting lymphocytes also offered protection

Types of immunity

1. Humoral Antibodies produced from lymphocytes

present in body as ‘humor’ 2. Cellular

Lymphocytes themselves defend the body

Antigens

Substances provoking an immune response (i.e. any foreign cell)

Not normally present in body, therefore ‘nonself’

Self recognition Major histocompatibility complex (MHC) class I

proteins - all cells except RBCs MHC class II proteins (on APC cells)

Humoral immunity

Humoral immunity

Clonal selection- Steps B-cells clone themselves upon encountering an antigen

(1° response, 3 - 6 days) Resulting plasma cells secrete antibodies into plasma Clone cells not differentiating into plasma cells become memory cells

Re-infection produces a 2° response

B-cell cloning

Humoral responses

Antibody structure Immunoglobulins (Ig)

4 polypeptides 2H, 2 L (disulphide bonds) Antibody monomer, T or Y shaped 2 antigen binding sites C (constant) region V (variable) region

Antibody classes

Classification based on C region in heavy chain IgD, IgG, IgE, IgA, and IgM

pentamerdimer

monomer

Antibody functions

Antibodies inactivate antigens and tag them for destruction

Strategies Neutralization Agglutination Precipitation Complement

Humoral immunity

Active - natural vs. artificially acquisition, memory B cells Long term protection

Passive - not challenged by antigens, no memory B cells Short term protection. From

mother several months, gamma globulin (gG) weeks.

Cells of adaptive immunity 1. Lymphocytes (B cells, T cells) T cells (immunocompetent in thymus)

B cells (immunocompetent in bone marrow)

Cells of adaptive immunity 2. Antigen-presenting cells (APC)

Engulf antigens, present fragments to Tc-cells to destroy

e.g. CT - dendritic cells, skin - Langerhans’ cells, lymph - macrophages

Cell-mediated immunity 2 types of T-cells, CD4

(TH) and CD8 (TC) T-cells activate by

double recognition V region binds to an

antigen, also recognize self (MHC class I proteins)

Cell-mediated immunity Helper T Cells

Bind to APC and help stimulate T cell and B cell proliferation using interleukin-2 (hormone)

Clinical connections 1. Organ transplants

Tissue similarity so that Tc cells, NK cells and antibodies do not attack the new organ

Immunosuppressive therapy Anti-inflammatory drugs Immunosuppressant drugs

2. Immunodeficiencies Immune cells, phagocytes, complement behave

abnormally AIDS/HIV - helper T cells destroyed

Clinical connections

3. Autoimmune diseases - loss of ability to distinguish self from non-self. Body produces antibodies against its own cells MS: destroys white matter of brain and spinal cord Type-1 diabetes: destroys pancreatic ß cells

4. Allergies Anaphylaxis: basophils and mast cells become

oversensitized to allergens, resulting in histamine release causing inflammation

Anaphylactic shock