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Chapter 16: The Adaptive Immune Response. Important Point:. If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!.

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Chapter 16: The Adaptive Immune Response

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important point
Important Point:

If you are having trouble

understanding lecture material:

Try reading your text

before attending lectures.

And take the time to read it well!

adaptive immunity

“In contrast to the innate immune response, which is always ready to respond to patterns that signify damage or invasion, the adaptive immune response matures throughout life, developing from the immune system arsenal the effective response against specific invaders as each is encountered.”

  • “An important hallmark of the adaptive immune response is that it has memory, a greatly enhanced response to re-exposure.”
  • Key to understanding adaptive immunity is the interactions between antigens and immune-system molecules, such as antibodies.
  • Also important is the concept of tolerance, which is the ability of the immune system to ignore common body molecules.
Adaptive Immunity
primary lymphoid organs

Theprimary lymphoid organs, are bone marrow and the thymus, where lymphocytes originate and/or mature (depending on type).

Primary Lymphoid Organs
secondary lymphoid organs

Thesecondary lymphoid organs, such as Lymph Nodes, are the sites of interaction among immune system cells including with antigens presented by Antigen Presenting Cells.

Secondary Lymphoid Organs

Antigen stands for Antibody Generator.

  • Antigens are molecules that are potentially recognized by adaptive immune-system molecules.
  • “Recognition” specifically means a binding between the antigen and the immune-system molecule, such as between a immunogen and an antibody.
  • Note, however, that an antigen within its “self” environment will not normally elicit (i.e., cause) an immune response.
  • To describe antigens found in non-self environments, the term Immunogen is more correct, though we won’t bother making this distinction.
  • An antigen consists of a number of recognizable regions known as Antigenic Determinants, a.k.a., Epitopes.
epitopes t depend antigen


Epitopes, T-Depend. Antigen







antigen antibody interaction
Antigen-Antibody Interaction

This is an individual antigen found on the surface of a virus. There are a number of chemically and physically distinct regions on it to which different antibody types (blue) might bind.

antigen antibody interaction1

Different antibodies produced by different B cells are able to attach to distinct epitopes found on the same or different antigens.

Antigen-Antibody Interaction
antibody a k a immunoglobulin
Antibody, a.k.a., Immunoglobulin

“Red Flag” = host-to-antibody binding region.

Note the two identical antigen-binding sites; both are contained within identical variable regions.

“Red Flag” = host-to-antibody binding region.

immunoglobulin in 3d
Immunoglobulin in 3D

Antigen-binding region.

Antigen-binding region.

And remember, an Antibody is not an “Antibiotic!!!!!”

“Red Flag” host to antibody binding region.

immunoglobulin classes

Longest lived Ab & present in colostrum.

Immunoglobulin Classes

Most abundant class (except in serum).

Associated with allergies.

immunoglobulin actions

Recall that C3b can bind directly to cell.

Prevents binding to host tissues.

Immunoglobulin Actions

Pilus as well as flagellum binding.

This is a host cell, covered with foreign antigens and therefore with antibody.

These are now available for phago-cytosis.

clonal selection theory

Applies to both B and T cells.

Takes place in 2° lyphoid organs.

Clonal Selection Theory

T cells are associated with cell-mediated immunity.

B cells are associated with Ab (Ig) production.

antigen presentation by b cell

Note binding by only one-half of the “Y”.

Antigen Presentation by B Cell

Results in production of Abs against T-Dependent Antigens (no T-helper binding, then no Ab).

if t binding then expansion
If T Binding then Expansion

Memory B cells = long-lasting immunity.

T-helper binding occurs here.

t independent antigens
T-Independent Antigens

Including carbohydrate portion of LPS.

pri sec immune response
Pri. & Sec. Immune Response

Clonal Expansion of Memory B cells—there are lots of ‘em!

Clonal Expansion of B cells.

pos neg t cell selection

Both T cells and B cells are derived fromhematopoieticstem cells found in bone marrow.

  • T cells migrate to the thymus for further development(and hence the “T” in T cells, though the “B” in B cells stands for Bursa).
  • T cells, during their development in the thymus, are subject to two round of selection.
  • The first round is Positive Selection where only T cells that can bind MHC are retained.
  • The second round is Negative Selection where T cells that recognize self antigens in association with MHC are deleted.
  • The resulting T cells, both helper and cytotoxic, consequently can bind MHC (II or I, respectively), but only if complexed with non-self antigens.
Pos & Neg T Cell Selection
antigen recognition by t cells
Antigen Recognition by T Cells

Recognition by Cytotoxic T cell (CD8 receptor)

Recognition by Helper T cell(CD4 receptor)

cytotoxic consequences
Cytotoxic Consequences

I.e., they tell their “friends” (other cytotoxic T cells).

Apoptosis is cellular suicide which here is induced by the CTL.

stimulating t helper cells
Stimulating T-Helper Cells

Macrophages and Dendritic cells present antigens to, and thereby stimulate, T-helper cells.