Serology Quiz #1

Innate Immunity

• Most primitive form of immunity

• General recognition

• first line of defense

• no previous exposure to antigen required

• nonspecific = physical and chemical mechanical barriers

Adaptive Immunity

• specific recognition of small portion of organism or triggering antigen

• generate memory of initiator

• should eliminate self-reacting cells

• two types: humoral and cell-mediated

Autoimmunity

Self-reacting cells persist and are not destoryed

T lymphocytes

CD4 and CD8 (2:1 ratio)

CD4 T cells

• helper T-cells

• can recognize MHC II protein molecules

• potent producers of cytokines

• Th1 and Th2

  • Th1 cells = produce IFN-g, IL2, TNF-b; protective against intracellular pathogens by activating macorphages and cytotoxic T cells

  • Th2 cells = produce IL4, IL5, IL6, IL10, IL13; help B cell regulation and antibody formation against extracellular pathogens

CD8 T cells

• cytotoxic T cells

• can recognize MCH I protein molecules

• kills tumor cells and infected macrophages

Major Histocompatibility Complex (MHC)

• must be on surface of antigen-presenting cell for T cell activation

• Class I MHC = on most cells, CD8 T cells

• Class II MHC or HLA-D antigens = only on antigen-presenting cells, dendritic cells, CD4 T cells

Epitope

specific site on the antigen to which antibody or T cell receptor can bind

one antigen can have many epitopes

Antibody Structure

Each monomer of antibody consist of

• 2 heavy chains = Fc region

  • complement fixation occurs at Fc region

• 2 light chains = Fab region

Isotope

portion of constant region of heavy chain that differs between Ig classes

Allotype

variation of alternative alleles at a single gene locus of constant region of heavy chains within a class

Idiotype

variation due to differences in both H and L chains variable regions (Fab portion)

unique to abs produced by single clone of B cells

IgG

• long-term immunity

• only Ig able to cross placenta

  • activated classical complement pathway

IgA

serum IgA = monomer

secretory A = dimer or tetramen with secretory pieceI

IgM

pentamer joined by J chain

can be found in low concentrations in secretions

effective activatory of the classical complement pathway

IgD

most IgD are membrane-bound to mature B cells

IgE

binds to mast cells and basophils at Fc

Fab binds allergen and causes degranulation of these cells

provides immune reponse to parasites

Primary Immune Response

IgM antibody appears first, followed by IgG on first exposure to antigen

Secondary Immune Response

follows re-exposure to same antigen

shorter response time

larger quantity of IgG produced

Classical pathway

antibody-dependent

components are numbered C1-C9

• recognition = C1

• activation = C2, C3, C4

• membrane attack complex (MAC) = C5-C9

Alternate pathway

antibody-independent

• cell walls of bacteria, fungi, viruses, and some parasites

C3, C5-C9 are same as classical pathway

Mannose-binding lectin (MBL) pathway

interaction of specific bacterial carbohydrates with complement components

Total hemolytic complement (CH50) assay

screening test for function of classical system based on ability of patient’s complement to lyse standarized amount anitbody coated sheep RBCs

AH50 Assay

screening test for alternate pathway function

rabbit blood cells can activate alternate pathway

if CH50 and AH50 are abnormal, defects in C3 or C5-C9

if CH50 abnormal, defect in C1, C4, or C2