Adaptive Immune SystemAdaptive Immune SystemAngela MitchellBIO42210/25/10mitcheam@email.unc.edu

““Jobs” of the Immune Jobs” of the Immune SystemSystem

““Jobs” of the Immune Jobs” of the Immune SystemSystemRecognize that invaders are present

◦Recognize that these are different than self

Recruit more cells/factors to fight invaders

Kill the invadersBlock any toxins produced by the

invadersLearn from past encounters to

increase future effectiveness

OVERVIEW OF HOST OVERVIEW OF HOST RESPONSE TO RESPONSE TO PATHOGENSPATHOGENS

Time Course of an Immune Time Course of an Immune ResponseResponse

Levels of the Immune Levels of the Immune ResponseResponse

Levels of the Immune Levels of the Immune ResponseResponse

Adaptive Responses Are Adaptive Responses Are Specific to Individual Specific to Individual MoleculesMoleculesAntigen: the molecule recognized

by the responseEach cell can only recognize one

antigen

Two Branches of Adaptive Two Branches of Adaptive ResponseResponseCellular immunity

◦ Main cells are T cells◦ Used against

intracellular pathogens

Humoral immunity◦ B cells and

antibodies◦ Used against

extracellular microbes and toxins

CELLULAR IMMUNE CELLULAR IMMUNE RESPONSERESPONSE

T cell Mediated Immunity

How do T cells recognize How do T cells recognize antigen?antigen?T cell receptorRecognizes small parts of

proteins “presented” on MHC molecules

MHC is present on antigen presenting cells

Starts with phagocytes Starts with phagocytes recognizing antigenrecognizing antigen

Antigen is processed and Antigen is processed and displayed: MHCIdisplayed: MHCI

Antigen is processed and Antigen is processed and displayed: MHCIIdisplayed: MHCII

Initial recognition by Initial recognition by pAPCspAPCsProfessional antigen presenting

cellsDendritic cells, macrophages,

and B cellOffer activating signals to T cells

—primes for activity

Types of T cellsTypes of T cellsCytotoxic T cells: CD8+ T cells

◦Recognize antigens on MHCI◦Releases granules to kills target cells

Helper T cells: CD4+ T cells◦Recognize antigens on MHCII◦Secrete cytokines to activate other

cells◦Two types: Th1 and Th2

Cytotoxic T cells (Tc)Cytotoxic T cells (Tc)

Helper T cells (Th)Helper T cells (Th)Th1 Cells: activate phagocytes

Th2 Cells: activate B cells

Concept QuestionConcept QuestionCytotoxic T cells are important for

defense from…

A. Bacteria onlyB. Intracellular pathogensC. Viruses onlyD. Fungus onlyE. Extracellular pathogens

Concept QuestionConcept Question

What do helper T cells recognize?

A. Exogenous peptides on MHCIB. Carbohydrates on bacteria cellsC. Exogenous peptides on MHCIID. Endogenous peptides on MHCIIE. Endogenous peptides on MHCI

HUMORAL IMMUNE HUMORAL IMMUNE RESPONSERESPONSE

B cell Mediated Immunity

B cells Produce AntibodiesB cells Produce AntibodiesDefense from extracellular

pathogens and toxinsRecognize antigen in native form

Activation of B cellsActivation of B cellsB cell receptor

(BCR) recognizes antigen

Th2 cells help activation

B cell differentiates to plasma cell

Produces antibodies

Antibody StructureAntibody StructureImmunoglobulins

(Ig)Functions

◦ Neutralize pathogens and toxins

◦ Lead to phagocytosis

◦ Activation of complement

Types of AntibodiesTypes of Antibodies

Types of AntibodiesTypes of Antibodies

Functional Activity

IgM IgD IgG IgA IgE

Neutralization + ++ ++

Phagocytosis + +++ +

Natural killer cell killing

++

Mast cell activation + +++Complement activation

+++ +++ +

Location BCR &Serum

BCR (minor)

Serum & tissue

Mucus & tissue

Mast cells

Concept QuestionConcept QuestionB cells recognize _____ with

membrane bound_____.

A. Peptides only MHCsB. Whole antigens MHCsC. Peptides only AntibodiesD. Carbohydrates only TLRsE. Whole antigens Antibodies

IMMUNOLOGICAL IMMUNOLOGICAL MEMORYMEMORY

Timing of Adaptive Timing of Adaptive ResponseResponse

Immunological MemoryImmunological Memory

Secondary Immune Secondary Immune ResponseResponse

Memory ResponsesMemory ResponsesSmall populations of B and T cells

retained from first exposureSurvive for a long time

Begin faster than first responseStronger than first response

IMMUNE SYSTEM IMMUNE SYSTEM SUMMARYSUMMARY

Adaptive Immune SystemAdaptive Immune System