Immunology Flashcards
Lymph node
- Site of B-cell localization
Outer cortex
Lymph node
- Primary follicle
- Secondary follicle
Primary follicle - Dense and dormant
Secondary follicle - Pale, germinal centers (proliferating B cells and follicular dendritic cells)
Lymph node
- Medullary cords: Cell types
B cells, plasma cells, macrophages
Lymph node
- Medullary sinuses: Cell types
Reticular cells, macrophages
Lymph node
- Site of T-cell localization
Paracortex
Lymph node
- Structure that is underdeveloped in Bruton (X-linked) agammaglobulinemia
Outer cortex - Primary/secondary follicles
Lymph node
- Structure that is underdeveloped in DiGeorge syndrome
Paracortex
Secondary lymph organ that initiates immune response to TISSUE-BORN antigens
Lymph node
Secondary lymph organ that initiates immune response to BLOOD-BORN antigens
Spleen
B cells
- Site of somatic hypermutation and isotype switching
Outer cortex of lymph nodes
B cells
- Site of antibody production and affinity maturation
White pulp of spleen
Spleen
- Site of B-cell localization
Follicles (white pulp)
Spleen
- Site of T-cell localization
Periarteriolar lymphatic sheath (PALS); white pulp
Clinical findings (4) post-splenectomy
- Howell-Jolly bodies (nuclear remnants)
- Target cells
- Thrombocytosis
- Lymphocytosis
Spleen is storage site for RBCs, platelets, and granulocytes
Splenectomy –> Loss of sequestration site for platelets (thrombocytosis) and granulocytes (lymphocytosis)
Encapsulated bacteria
SHiNE SKiS
Streptococcus pneumoniae Haemophilus influenzae type b Neisseria E. coli Salmonella Klebsiella pneumoniae Group B streptococci
Mechanism by which splenic dysfunction increases susceptibility to encapsulated organisms
Spleen responsible for 50% antibody production
Decreased IgM –> Decreased complement activation –> Decreased C3b –> Decreased opsonization of encapsulated bugs –> Increased susceptibility
Encapsulated bugs are resistant to phagocytosis
Site of immune response initiation in the spleen
Marginal zone
Embryologic origin of thymus
Third pharyngeal pouch (endoderm)
Embryologic derivation of T cells
Mesoderm
Thymic cortex
Dense - Immature T cells
Thymic medulla
Pale - Mature T cells
Structure in thymic medulla believed to be site of destruction of T cells that improperly matured
Hassall corpuscles (“whorls” of reticular cells)
Structure responsible for ensuring antigen-free environment in which immature T cells develop
Blood-thymus barrier
MHC class I and II molecules encoded by HLA genes on chromosome ___
Chromosome 6
MHC class I - HLA types (3)
HLA-A, HLA-B, HLA-C
MHC class II - HLA types (3)
HLA-DP, HLA-DQ, HLA-DR
Cells that express MHC class I molecules
All nucleated cells + platelets
NOT RBCs
Cells that express MHC class II molecules
APCs
MHC class I molecules present ___ synthesized antigens to ___ T cells
Endogenously synthesized antigens to CD8+ cytotoxic T cells
Self antigens, tumor antigens, viral antigens
Virus uses host cell machinery to translate proteins, which eventually are degraded by proteasomes and loaded onto MHC I
MHC class II molecules present ___ synthesized antigens to ___ T cells
Exogenously synthesized antigens to CD4+ T cells
Bacterial antigens
Antigen loading onto MHC class I molecules
Antigenic peptide fragments translocated via transporter (TAP complex) into rER where loaded onto MHC I
Antigen loading onto MHC class II molecules
Transport vesicle carrying MHC II fuses with phago- or endolysosome carrying antigenic peptides
Acidic environment displaces invariant chain from binding site on MHC II and permits antigen binding
Unique protein a/w MHC I
Beta-2 microglobulin, which directs MHC I transport to cell surface
Unique protein a/w MHC II
Invariant chain, which inhibits binding of self-antigens until fusion with phagolysosome containing antigenic peptides
Unique NK cell marker
CD56+
NK cell marker that functions in ADCC
CD16+ = membrane receptor for Fc region of IgG
NK cells target tumor cells and virally-infected cells with
Decreased/absent MHC class I expression
NK cells employ 2 receptor types critical for their cytotoxic function
One delivers a stimulatory (kill) signal
One delivers an inhibitory (don’t kill) signal
Inhibitory signal binds MHC class I
Tumor cells and virally-infected cells that lack MHC class I expression receive only the stimulatory (kill) signal
Cytokines (4) that activate NK cells
- Cytokines and source
Virally infected cells: IFN-alpha, IFN-beta
T cells: IL-2
Macrophages: IL-12
B cell receptor
- # idiotypes per cell
- # isotypes per cell
- # antigen-binding sites
Idiotype = Antigen-binding site
1 idiotype 2 isotypes (IgM, IgG) 2 antigen-binding sites (valence = 2)
T cell receptor
- # idiotypes per cell
- # isotypes per cell
- # antigen-binding sites
Idiotype = Antigen-binding site
1 idiotype 1 isotype (α/β) 1 antigen-binding site (valence = 1)
B cell receptor
- Glycoprotein components
Heavy chain (2) + light chain (2)
T cell receptor
- Glycoprotein components
α chain + β chain
B cell receptor
- Components of signal transduction complex
Igα, Igβ, CD19, CD21
T cell receptor
- Components of signal transduction complex
CD3
T cell development
- Differentiation/development that occurs in the subcapsular zone of the thymus (2)
(1) Beta-gene rearrangement (TCR)
(2) Co-expression of CD4 and CD8
Double negative –> Double positive
T cell development
- Differentiation/development that occurs in the cortex (2)
(1) Alpha-gene rearrangement (TCR)
- -> Functional alpha/beta TCR
(2) Positive selection
Positive selection
Cortical epithelial cells (thymus) express self MHC antigens that interact with TCR of immature thymocytes in CORTEX
Able to bind self MHC –> Positive selection
Unable to bind self MHC –> Failure of positive selection –> Apoptosis
T cell development
- Differentiation/development that occurs in the medulla (1)
Negative selection
Negative selection
Medullary epithelial and dendritic cells (thymus) express self MHC antigens that interact with TCR of immature thymocytes in MEDULLA
Bind self MHC too strongly –> APOPTOSIS
Central tolerance
Tolerance = Immunologic unresponsiveness to self antigens
CENTRAL TOLERANCE acquired in the thymic medulla during negative selection
Peripheral tolerance
Tolerance = Immunologic unresponsiveness to self antigens
PERIPHERAL TOLERANCE develops by T CELL ANERGY, which is the functional inactivation of T cells that react to self antigen
