L3: ANTIGENS AND MHC

immunogen

• triggers (induces) an adaptive immune response causes the production of antibodies (via b cells), or sensitized t cells

antigen

• can bind to antibodies or t cells

• may not be able to trigger an immune response by itself

• something the immune system can recognize

epitopes

• specific molecular shape or configuration on an antigen that is recognized by b or t cells

• aka antigenic determinant

haptens

• are small molecules that are not immunogenic by themselves

• become immunogenic when attached to a carrier proteins

• this creates new antigenic determinants

autoantigens

• self

• dna, rbc antigens

alloantigens

• other humans

• blood group antigens

heteroantigens

• other species

• bacterial proteins

heterophile antigens

• unrelated species with similar structures

• im test

major histocompatibility complex

• is a group of genes that code for hla molecule

• these molecules exist on almost all nucleated cells

• determine tissue compatibility

• control t-cell activation

• are essential for both humoral and cell-medicated immunity

• t cells can only recognize when it is presented on mhc molecules

class 1

• hla-a, hla-b, hla-c

• antigen presentation to cd8 t cells

class 2

• hla-dr, hla-dq, hla-dp

• antigen presentation to cd4 t cells

class 3

• between 1 and 2

• codes for complement proteins, tnf, cytokines

class 1 pathway

• all nucleated cells

• alpha chain (45 dka) > polymorphic

• b2-microglobulin (12 dka) > non-polymorphic

• three external domains: a1, a2, a3

• peptide-binding groove between a1 and a2

• binds peptides 8-10 amino acids long

class 2 pathway

• only on antigen-presenting cells: (dendritic cells, macrophages, monocytes, b cells)

• alpha chain + beta chain

• binding groove between a1 and b1

• groove is open at both ends

• binds peptides 13-18 amino acids

hla b27

• ankylosing spondylitis (strongest association), reactive arthritis (reiter syndrome), psoriatic arthritis, enteropathic arthritis, acute anterior uveitis

hla dr2

• multiple sclerosis, goodpasture syndrome, narcolepsy

hla dr3

• systematic lupus erythematosus, type 1 diabetes mellitus, graves disease, myasthenia gravis, hashimoto thyroiditis

hla dr4

• rheumatoid arthritis, type 1 diabetes mellitus, addison disease

hla dr5

• hashimoto thyroiditis, pernicious anemia

hla dq2/dq8

• celiac disease, type 1 diabetes mellitus

hla b8

• myasthenia gravis, graves disease, addison disease, celiac disease, selective iga defieciency

hla dr1

• rheumatoid arthritis

hla dr7

• type 1 diabetes mellitus, celiac disease