Immunology Flashcards
Positive selection location
thymic cortex
Negative selection location
Thymic medulla
MHC class II deficiency
/defect in development of CD4+ cells in the thymus. /no MHC class II so helper cells cannot be selected by positive selection mechanisms in the thymus but CD8 cytotoxic cells can be produced. /also known as type II bare lymphocyte syndrome.
Positive selection mechanism
T cells expressing TCRs capable of binding self-MHC on cortical epithelial cells survive.
Negative selection mechanism
T cells expressing TCRs with high affinity for self antigens undergo apoptosis. Tissue-restricted self-antigens are expressed in the thymus due to the action of autoimmune regulator (AIRE).
Autoimmune polyendocrine syndrome-1
deficiency of negative selection.
Lymph drainage of head and neck
cervical
Mediastinal lymp nodes drain
trachea and esophagus
Axillary lymph node drainage
Upper limb, breast, skin above umbilicus
Celiac lymph node drainage
Liver + stomach + spleen + pancreas + upper duodenum
Superior mesenteric lymph node drainage
lower duodenum + jejunum + ileum + colon to splenic flexure
Inferior mesenteric lymph node drainage
Colon from splenic flexure to upper rectum
Internal iliac drains
Lower rectum to anal canal (above pectinate line) + bladder + vagina (middle third) + cervix + prostate
Para-aortic drains
testes + ovaries + kidneys + uterus
Superficial inguinal node drains..
anal canal (below pectinate) + skin below umbilicus (except popliteal area) + scrotum + vulva.
popliteal drains
dorsolateral foot + posterior calf
thoracic duct drains into..
junction of left subclavian + internal jugular veins
Function of medullary sinus of lymph node
Outside near capsule. Houses reticular cells and macrophages, which perform nonspecific filtration.
Location of B-cells in lymph node
Outer cortex.
lymph node follicle
Site of b-cell localization and proliferation
Difference between primary follicles and secondary follicles.
Primary follicles are dense and dormant, secondary follicles are activated and have pale central germinal centers.
Function of medulla of lymph node and composition
Consists of medullary cords and medullary sinuses.
Medullary cords
Closely packed lymphocytes and plasma cells.
medullary sinuses
Communicate with efferent lymphatics and contain reticular cells and macrophages.
Where are T cells located in lymph node?
paracortex
Paracortex
region between follicles and medulla. Contains high endothelial venules through which T and B cells enter from blood.
Sinusoids of spleen
Long, vascular channels in red pulp with fenestrated “barrel hoop” basement membrane.
Where are T cells found in the spleen?
periarteriolar lymphatic sheath (PALS) within the white pulp.
Where are B cells found in the spleen?
Follicles within the white pulp.
Marginal zone of spleen.
Zone between the red pulp and white pulp that contains macrophages and specialized B cells.
Marginal zone of spleen function
Where APCs capture blood-borne antigens for recognition by lymphocytes.
GBS encapsulated or nonecapsulated?
encapsulated
Mechanism for increased susceptibility to encapsulated organisms with splenic dysfunction
Decreased IgM –> decreased complement activation –> decreased C3b opsonization.
Postsplenectomy hematologic findings
1) Howell-Jolly bodies (nuclear remnants)
2) Target cells
3) Thrombocytosis (loss of sequestration and removal)
4) lymphocytosis (loss of sequestration).
Spleen follicle organization
Germinal center surrounded by mantle zone surrounded by marginal zone.
Thymus location
Anterosuperior mediastinum
Thymus organization
Cortex is dense with immature T cells; medulla is pale with mature T cells and Hassall corpuscles
Hassall corpuscles
Contain epithelial reticular cells
T cell and B cell origin
T cells = Thymus (mature in thymus, originate in bone marrow), B cells = Bone marrow.
Thymic hypertrophy seen in…
MG
Innate immunity components
Neutrophils, macrophages, monocytes, dendritic cells, NK cells (lymphoid origin), complement.
Mechanism of innate immunity
Germline encoded
What physical barriers does innate immunity have?
epithelial tight junctions + mucus
Proteins secreted by innate immunity
lysozyme, complement, CRP, defensins.
Key features of pathogen recognition in innate immunity
Toll-like receptors (TLRs).
TLRs
Pattern recognition receptors that recognize pathogen-associated molecular patterns (PAMPs) (eg LPs, flagellin, nucleic acids (viruses))
Components of adapative immunity
T cells, B cells, circulating antibodies
MHC 1 loci
HLA-A, HLA-B, HLA-C (all have 1 letter)
MHC 1 expression
Expressed on all nucleated cells. Not expressed on RBCs.
MHC I vs. MHC II function
MHC 1 present endogenously synthesized antigens (eg viral or cytosolic proteins) to CD8+ T cells. MHC II prsent exogenously synthesized antigens (eg bacterial proteins to CD4+ helper T cells).
protein associated with MHC 1
Beta2-microglobulin
Antigen loading in MHC 1
Antigen peptides loaded onto MHC I in RER after delivery via TAP (transporter associated with antigen processing).
MHC II loci
HLA-DP, HLA-DQ, HLA-DR (all have 2 letters)
MHC II expression
Expressed on APCs
protein associated with MHC II
Invariant chain
Mechanism of MHC II
Antigen loaded following release of invariant chain in an acidified endosome.
HLA A3
hemochromatosis
Addison disease HLA association
B8
MG HLA association
B8
MS HLA association
DR2
RA HLA association
DR4
Addison’s HLA association
DR3 + DR4
Hashimoto’s HLA association
DR5
DM1 HLA association
DR3 + DR4
MS HLA association
DR2
Goodpasture’s HLA association
DR2
SLE HLA association
DR2 + DR3
Pernicious anemia HLA association
DR5
Hay fever HLA association
DR2
Graves HLA association
DR3
NK cell mechanism
Use perforin and granzymes to induce apoptosis of virally infected cells and tumor cells
What enhances NK cell activity?
IL-2 + IL-12 + IFN-alpha + IFN-beta
What induces NK cells?
Exposure to a nonspecific activation signal on target cell and/or to an absence of class I MHC on target cell surface.
NK cell other mechanism
antibody-dependent cell mediated cytotoxicity
antibody-dependent cell mediated cytotoxicity mechanism
CD16 binds Fc region of bound Ig, activating NK cell
Process of B cell antigen specificity
somatic hypermutation
CD4+ vs. CD8+ cells
CD4 help b cells make antibodies and produce cytokines to recruit phagocytes and activate other leukocytes. CD8 directly kill virus-infected cells.
Where are mature and immature T cells found?
immature in cortex, mature in medulla.
What activates Th1 cells?
IL-12
What activates Th2 cells?
IL-4
What activates Th17 cells?
TGF-beta + IL-6
What are cytotoxic T cells activated by?
Th1 cells
What induces differentiation of Th1 cells?
IFN-gamma and IL-12
What inhibits TH1 cells?
IL-4 + IL-10 (from Th2 cell)
What do Th2 cells secrete?
IL-4, IL-5, IL-10, IL-13
Th2 cell function
Recruit eosinophils for parasite defense and promote IgE production by B cells
What induces differentiation of Th2 cells?
IL-4
What inhibits Th2 cells?
IFN-gamma from Th1 cells
macrophage-lymphocyte interaction mechanism
Macrophages and other APCs release IL-12, which stimulates T cells to differentiate into Th1 cells. Th1 cells release IFN-gamma to stimulate macrophages.
Cytotoxic T cell mechanism
1) kill virus-infected, neopalstic, and donor graft cells by inducing apoptosis.
2) release cytotoxic granules containing preformed proteins (eg perforin, granzyme B)
Regulatory T cell mechanism
Maintain specific immune tolerance by suppressing CD4 and CD8 T-cell effector functions.
Regulatory T cell markers
CD3, CD4, CD25, FOXP3
What do activated regulatory T cells produce?
anti-inflammatory cytokines (IL-10 + TGF-beta)
APCs
B cells + macrophages + dendritic cells
Caveat about T and B cell activation
Two signals are required for T-cell activation, B-cell activation, and class switching.
Naive T-cell activation
Dendritic cell samples and processes antigen –> dendritic cell migrates to draining lymph node –> T-cell activation (signal 1): antigen is presented on MHC II and recognized by TCR on Th (CD4+) cell. Endogenous antigen is presented on MHC I to Tc (CD8+) cell –> Proliferation and survival (signal 2): costimulatory signal via interaction of B7 proteins (CD80/86) and CD28 –> Th cell activates and produces cytokines. Tc cell activates and is able to recognize and kill virus-infected cell.
B-cell activation and class switching mechanism
- Th-cell activation.
- B-cell receptor-mediated endocytosis; foreign antigen is presented on MHC II and recognized by TCR on Th cell.
- CD40 receptor on B cell binds CD40 ligand (CD40L) on Th cell.
- Th cell secretes cytokines that determine Ig class switching of B cell. B cell activates and undergoes class switching, affinity maturation, and antibody production.
Fab
region of antibody containing variable/hypervariable regions.
What fixes comploment
Fc region of IgM and IgG
Idiotype
unique antigen-binding pocket; only 1 antigenic specificity expressed per B cell.
carbohydrate side chains
Expressed on Fc region
What determines isotype (IgM, IgD, etc)?
Fc region
neutralization
Antibody binding and preventing bacterial adherence.
VJ
light-chain genes
V(D)J
heavy-chain genes
How is antibody diversity generated?
1) Random recombination of VJ (light-chain) or V(D)J (heavy-chain) genes.
2) random addition of nucleotides to DNA during recombination by terminal deoxynucleotidyl transferase (TdT)
3) Random combination of heavy chains with light chains
How is antibody specificity achieved?
1) Somatic hypermutation and affinity maturation (variable region)
2) Isotype switching (constant region)
Affinity maturation mechanism
Process by which Th cell-activated B cells produce antibodies with increased affinity for antigen. With repeated exposures to the same antigen, host produces antibodies of successively greater affinities.
Immunoglobulins expressed on mature, naive B cells prior to activation…
IgM and IgD
What mediates isotype switching?
CD40L and cytokines
Immunoglobulin responsible for neutralizing bacterial toxins and viruses
IgG
Main antibody in secondary (delayed) response to an antigen
IgG
Which immunoglobulins have J chains?
IgA and IgM
IgA in circulation
Exists as a monomer
How does IgA cross epithelial cells?
Transcytosis
IgA caveat
Most produced antibody overall, but has lower serum concentrations.
What contains IgA
Tears, saliva, mucus, and breast milk.
What is secretory component?
Portion of IgA that IgA picks up from epithelial cells, and which protects Fc portion from luminal proteases.
What is produced in the immediate response to an antigen?
IgM
IgM forms
Monomer on B cell, pentamer with J chain when secreted.
Why does IgM exist as a pentamer?
Pentameric form enables avid binding to antigen while humoral response evolves.
IgD
Unclear function. Found on surface of many B cells and in serum.
What immunoglobulin has the lowest concentration in serum?
IgE
Thymus-independent antigens
Antigens lacking a peptide component. Thus, they can’t be presented by MHC to T cells and are weakly immunogenic.
Example of thymus-independent antigen
LPS
Critical function of CD40L
Class-switching. Expressed on helper T cells
What activates acute-phase reactants?
IL-6
What produces acute-phase reactants
liver
CRP function
Opsonin; fixes complement and facilitates phagocytosis
CRP clinical significance.
Sign of ONGOING inflammation.