IMMUNOLOGY

By ZOHA and SAMIHA

Our learning objectivespay attention – we will test you!

• Types of immune responses and cells involved• Definitions :Learn them all but make sure you

understand affinity vs avidity • CD markers, APCs… lots of letters but they will

make sense!• Innate immunity – COMPLEMENT • Antibodies

TYPES OF IMMUNITY

• INNATE immunity1) Broad specificity

(require Pattern Recognition Proteins)

2) Anatomical and Physiological barriers

3) Rapid response4) NO immunological

memory

• ACQUIRED immunity1) Antigen specific2) Slower response3) Involves

immunological memory

** Innate immune system directs the acquired immune system

INNATE IMMUNE SYSTEMTHIS IS THE EARLY PHASE RESPONSE TO PATHOGEN

INVASION

CELLULAR COMPONENTS HUMORAL COMPONENTS

NEUTROPHILS CYTOKINES

NATURAL KILLER cells COMPLEMENT

MONOCYTES/ MACROPHAGES ANTI MICROBIAL Peptides

MAST cells

DENDRITIC cells

NB- some cellular and humoral factors of the innate system are also involved in the adaptive system

The Key PlayersNEUTROPHILS

(PMN):• Blood Tissue via

DIAPEDESIS and CHEMOTAXIS

• PHAGOCYTOSIS

This is aided by the process of OPSONISATION

• KILLINGOxygen dependent/independent

MACROPHAGES:• Monocytes (blood)

Macrophages (tissue)

• Express pattern recognition molecules

• Become activated by molecular patterns on

bacterial surface

PHAGOCYTOSIS CYTOKINE RELEASE

WHAT HAPPENS IN SYSTEMIC INFECTION???

BACTERIAL SEPTIC SHOCK

COMPLEMENT SYSTEMCLASSICAL PATHWAY

ALTERNATIVE PATHWAY

ANTIBODY INDEPENDENT/ LECTIN PATHWAY

C3

MEMBRANE ATTACK COMPLEXES

OPSONISATIONLYSIS

DEGRANULATION OF MAST CELLS

LEUKOCYTE RECRUITMENT

1)

2)

3)

** BUT THIS IS LIKE AN ENZYME CASCADE SYSTEM – small input gives BIG outputSO WE NEED TO CONTROL THIS SYSTEM

A TYPICAL LOCAL ACUTE INFLAMMATORY RESPONSE

LOCAL ACUTE to SYSTEMIC ACUTE PHASE response

• CYTOKINE INDUCED

FEVER LEUKOCYTOSISACUTE PHASE

PROTEINS IN LIVER

1. CRP2. MBL3. SERUM AMYLOID 4. COMPLEMENT

*Complement activation by Lectin pathway

ADAPTIVE IMMUNE RESPONSE

CELLULAR COMPONENTS HUMORAL COMPONENTS

MONOCYTES/ MACROPHAGES COMPLEMENT

DENDRITIC CELLS CYTOKINES

MAST CELLS ANTIBODIES

LYMPHOCYTES

THIS IS THE SPECIFIC, ANTIGEN MEDIATED IMMUNITY

LYMPHOCYTES

• PRODUCED IN THE PRIMARY LYMPHOID ORGANS in HEMATOPOESIS

BONE MARROW THYMUS

* So how does the body ensure that these naive lymphocytes interact with complimentary antigens?

• INTERACTION WITH ANTIGEN OCCURS IN SECONDARY LYMPHOID ORGANS

SPLEEN LYMPH NODES MALT eg Peyer’s Patches

LYMPHOCYTES

B- Lymphocytes• Express CD19 and CD20• Express Surface Antigen

Receptor (Ig molecule).• Express MHC class II

molecules to “present” antigens to T cells.

• Produce antibodies to mount an immune response.

T- Lymphocytes• All express CD3. • 2/3 express CD4 (helper T cells)

which secrete cytokines.• 1/3 express CD8 (cytotoxic T cells)

which are responsible for lysing infected cells and also producing cytokines.

• Recognise processed antigen presented by APCs with MHC class II.

APCs• B cells (present to T cells)• Dendritic cells (present to T cells)• Follicular Dendritic cells (present to B cells)• Activated Macrophages (present to T cells)

Antibodies• Work by: Complement activation, opsonisation or cell

activation by antibody-binding receptors. • Define Affinity: strength of an individual bond between an

antigen and an antibody • Define Avidity: overall strength of all the bonds.• This means IgM – which has more binding sites – will have a

greater avidity that IgG, which may have greater affinity.• G – 4 subclasses. Most abundant. Placental transfer• A – 2 subclasses. Secretory. Dimer• M – agglutination in a primary response. Pentameric

molecule. • E – parasites/allergies. Bound to mast cells &

basophils=histamine release. • D – involved in B cell development.

MCQs

• ALL T cells express the CD3 marker • Lysozyme is present in tears• IgG antibodies are more efficient at

agglutination than IgM antibodies • IgE is useful for passive immunity• MALT is lymphoid tissue• antibody-antigen complexes activate the

classical pathway of complement

• T

• T

• F

• F• T

• T

Take home points• This was just an overview of some areas – there

are lots of other details to remember that you just need to get under your belt.

• Definitions – learn them basically but make sure you understand first.

• Innate immunity – Complement – but you should also look over acute phase response, learn the proteins involved and try to integrate everything.

• Antibodies – we just gave you a way to remember but you will need to learn the details.