Lecture 14

Immunology:

Adaptive Immunity

Principles of Immunity• Naturally Acquired Immunity- happens

through normal events• Artificially Acquired Immunity- by

immunization• Active Immunity- result of an immune

response in an individual exposed to antigen

• Passive Immunity- occurs naturally during pregnancy; or antibodies from one person transferred to another

• Innate Immunity- Immunity that we are born with

Figure 17.1

Adaptive Immunity

• Different from Innate Immunity

• Matures throughout life

• Develops specific immune response as invaders are encountered

• Has a “memory”

• Must discriminate between self and dangerous (non-self)

• Very complex system

Adaptive Immunity

• Four important attributes:• Specificity- immune system responds

specifically to epitopes

• Tolerance of “self”- Immune system does not respond to “self”

• Minimal “self” damage- do not damage “self”

• Immunologic Memory- Once exposed will not get sick with same disease again

Overview of Adaptive Immunity

• Uses two basic strategies

1. Humoral Immunity

- works to eliminate antigens that are extracellular

1. Cellular Immunity

- deals with antigens within host cell

Humoral Immunity

Overview of Humoral Immune Response

• Mediated by B-lymphocytes or B-cells

• Encounter antigen- differentiate and proliferate into plasma cells and memory B cells

• Plasma cells make Y-shaped molecules called antibodies

• Antibodies bind to antigens, providing protection to host

Antibodies

• Globulin protein molecules- also called Immunoglobulins

• Secreted by B-cells

• Y-shaped

• 5 different classes:– IgM, IgG, IgA, IgE, IgD

Figure 17.3 - Overview

Table 17.1

Immunoglobulin M (IgM)

• First class produced during primary immune response to antigen

• It is in pentamer form

• Large- does not cross from blood to tissues

Immunoglobulin G (IgG)

• 80-85% of total Ig’s in people over age 2• Provides longest term protection of all

antibodies• First and most abundant Ig, during

secondary response• Can cross placenta from mother to fetus-

helps to protect fetus and new-born• Also present in colostrum- first breast-milk

produced

Immunoglobulin A (IgA)

• Important in mucosal immunity• In breast milk- protects infants from

intestinal pathogens

Immunoglobulin D (IgD)- Accounts for less than 1% of Ig’s- Involved in development and maturation of

antibody response

Immunoglobulin E (IgE)

• Barely detectible in blood

• Bound tightly to basophils and mast cells

• Bound IgE, allows these cells to detect and respond to antigens

• These cells release histamine, cytokines, and other chemicals that contribute to immune response

Allergies

• Basophils and mast cells release their chemicals when IgE binds to normally harmless material such as pollens

• Leads to immediate reaction- coughing, sneezing, and muscular contractions

• Response can be life threatening

Primary and Secondary Responses of Antibodies

Protective Outcomes of Antibody-Antigen binding

A. Viral Inhibition: virus preventing it from attaching to cell

B. Neutralization: make toxins unable to bind to cells

C. Opsonization: antibodies bind to antigen and facilitate attachment of phagocytic cells

D. and E. Agglutination and Precipitation: antibodies bind to antigen and get them into clumps, then one big “mouthful” for phagocyte

F. Phagocytosis: Fc portion of antibody encourages phagocytosis

Complement Activation: binding of antigen to antibody can trigger one pathway of complement cascade

B-cells and Antibody Response

• B-cell receptor binds to antigen

• One of two things happen:– B-cell needs confirmation by T-cell to begin

responding– B-cell does not need confirmation by T-cell to

begin responding

When B-cell does not need confirmation from T-cell

• B-cell receptors bind epitopes

• B-cells respond by proliferating, producing antibody and differentiating into memory B-cells

Fi When B-cell needs confirmation from T-cell gure 16.9

Cellular Immunity

Overview of Cellular Immunity

• Mediated by T lymphocytes or T-cells

• Has receptor similar to B-cells

• Antigen must be presented to it by another cell

• Two types:– T-cytotoxic cells- destroy infected cells– T-helper cells- activate macrophages

T-cells: Antigen Recognition and Response

• Have multiple copies of receptor on surface that recognizes specific antigen

• DO NOT produce antibody• DOES NOT interact with free antigen• Antigen must be presented by another

cell, by MHC • Two types of T-cells:

– T-cytotoxic– T-helper

Figure 16.15

T-cytotoxic cells

• Also called CD8 T cells

• Once activated, induce apoptosis in “self” cells infected with virus; destroy cancerous host cells

• Distinguish infected “self” cells, because these cells present peptides on surface in MHC class I molecule

Figure 17.10 - Overview

T-helper cells

• Also called CD4 T-cells

• Antigen presenting cells, present antigen to T-helper cells in MHC class II

• If recognize antigen presented as foreign, activate macrophages, release cytokines that recruit other cells of immune system, stimulate NK cells, activate B cells

Figure 17.9 - Overview (1 of 4)