Immunology Flashcards
What the primary lymphoid organs?
Thymus and Bone marrow
What is the function of lymph nodes?
nonspecific filtration by macrophages, storage and activation of B and T cells. Ab production
What does the structure of a lymph node look like?
- many afferents, one efferent
- encapsulated w/ trabeculae
- follicle, medullar, and paracortex
What is found in the follicle of a lymph node?
site of B cell localization and proliferation
- in outer cortex - primary follicles are dense and dormant. Secondary follicles have pale central germinal centers and are active
What is found in the medullar of a lymph node?
- medullary cords (closely packed lymphocytes and plasma cells
- medullary sinuses - communicated w/ efferent lymphatics and contain reticular cells and macrophages
What is found in the paracortex?
- T cells
- this is the region btw follicles and medulla
- contains high endothelial venules through which T and B cells enter from blood
What happens to the paracortex in an intense immune response?
becomes greatly enlarged
What happens to the paracortex in DiGeorge pts?
not well developed b/c they don’t have T cells
What is the lymphatic drainage from the following areas of the body?
- Upper limb, lateral breast
- stomach
- duodenum, jejunum
- sigmoid colon
- rectum (lower portion) of anal canal (above pectinate line)
- anal canal below the pectinate line
- testes
- scrotum
- thigh
- lateral side of dorsum of foot
- axillary
- Celiac
- superior mesenteric
- colonic – inferior mesenteric
- internal iliac
- superficial inguinal
- superficial and deep plexuses –> para aortic
- superficial inguinal
- superficial inguinal
- popliteal
What is considered to be the largest component of the immune system?
MALT - made up by GALT, NALT, BALT, genitourinary tract, appendix, tonsils, adenoids, M cells
What are M cells?
- found in the mucous membranes of small gut
- ## flattened epithelial cells lacking microvilli. there are deep pockets on the basilar side that allow Ag presentation to dendritic cells, B and T cells, and macrophages
What are Peyer’s patches?
- unencapsulated lymphoid tissue
- found in lamina propria and submucosa of small gut
- B cells make IgA
What does the right lymphatic duct drain?
-right arm, right chest, and right half of head
What does the thoracic duct drain?
everything else
Where does the thoracic duct drain?
junction b/w lespift subclavian and internal jugular vein
Describe the sinusoids of the spleen?
long, vascular channels in red pulp w/ fenestrated barrel hoop basement membrane. Macrophages found nearby
Where are T cells found in the spleen?
Periarterial lymphatic sheath (PALS) within the white pulp
Where are the B cells found in the spleen?
follicles w/in the white pulp
What is the role of the macrophages in the spleen?
remove encapsulated bacteria
What happens when there is splenic dysfunction?
- decreased IgM = decreased complement activation = decreased C3b opsonization
- increases susceptibility to encapusulated organisms
What are some encapsulated organisms that you need to worry about when you have splenic dysfunction?
E coli, pseudomonas, strep pneumoniae, Haemophilus influenzae type B, Nessiera meningitidis, salmonella, klebsiella, cryptococcus neogformans, group B Strep
Where are situations that a splenic dysfunction will take place?
- sickle cell pts
- Trauma to spleen
- hereditary sphereocytosis
What happens after postsplenectomy?
- Howell Jolly bodies - nuclear remnants
- Target cells
- Thrombocytosis
What is important about the thymus?
- site of T cell differentiation and maturation
- encapsulated
- from epithelium of 3rd branchial pouch
- Cortex is dense w/ immature T cells
- Medulla is pale w/ mature T cells and epithelial reticular cells containing Hassall’s corpuscles.
What is innate immunity?
- response to pathogens is fast and nospecific
- no memory
- consists of neutrophils, macrophages, dendritic cells, natural killer cells, and complement
What is adaptive immunity?
- receptors that recognize pathogens undergo VDJ recombination during lymphocyte development
- Response is slow on first exposure but memory response is faster and more robust.
- Consists of T and B cells and circulating Abs
What is the MHC?
major histocompatibility complex
- encoded by human leukocyte antigen (HLA) genes
- presents Ag fragment to T cells and TCR
What are the genetics for MHC I?
HLA A, B, and C
What cells have MHC I?
expressed on all nucleated cells. not expressed on RBC
What does MHC I bind to?
TCR and CD8
How does MHC I work?
- mediates viral immunity
- pairs w/ Beta 2 microglobulin (aids in transport to cell surface)
- Ag is loaded in RER w/ mostly intracellular peptides
What genes are associated w/ MHC II?
HLA DR, DP, and DQ
What receptors does MHC II bind to?
binds TCR and CD4
what cells have MHC II?
expressed only on APCs
How does MHC II work?
Ag is loaded following release of invariant chain in an acidified endosome
What are the following HLA genes associated with?
- A3
- B27
- DQ2/8
- DR2
- DR3
- DR4
- DR5
- hemochromatosis
- Psoriatic arthritis, ankylosing spondylitis, inflammatory bowel disease, reiter’s syndrome – (PAIR)
- Celiac disease
- MS, hay fever, SLE, goodpasture’s
- DM type 1, Grave’s disease
- RA, DM type 1
- Pernicious anemia –> B12 deficiency, Hashimoto’s thyroiditis
How do natural killer cells work?
they use perforin and granzyme to induce apoptosis of virally infected cells and tumor cells.
- it’s the only lymphocyte member of innate immune system
What cytokines enhance natural killer cells?
IL2, IL12, IFN-beta, and IFN -alpha
When are natural killer cells induced to kill?
- when exposed to a nonspecific Ag signal on target cells
2. an absence of class I MHC on target cell surface
What are the surface makers for natural killer cells?
CD 16, CD 56
What does CD16 do?
it binds to constant region of Abs
- found on NK cells and phagocytes to help them recognize and kill Ig coated cells by Ab dependent cell mediated cytotoxicity (ADCC)
What are the major functions of B cells?
- make Abs
2. used in hyperacute and humorally mediated acute and chronic organ rejection
What are the roles of Abs?
- opsonize bacteria
- neutralize viruses (IgG)
- activated complement (IgM, IgG)
- sensitize mast cells (IgE)
What are the major functions of T cells?
- CD4 T cells help B cells make Ab and produce cytokines to activate other cells of immune system
- CD8 cell kill virus-infected cells directly
- involved in cell-mediated HSR (type 4)
- Acute and chronic cellular organ rejection
What are all the APCs of the body
- M cells in gut
- Dendritic cells in the skin
- Macrophages
- B cells
What are the steps of T cell differentiation?
- immature T cells in bone marrow travel to the thymus
- Positive and negative selection takes place in corticomedullary junction
- the matured cells like in the lymph nodes and wait to be activate
What happens during positive selection of T cells?
T cells expressing TCRs capable of binding surface self MHC molecules survive
What happens during negative selection of T cells?
T cells expressing TCRs / high affinity for self Ag undergo apoptosis
What cytokines help differentiate Helper T cells to become either Th1 or Th2 cells?
- to make Th1 cells, you need IL 12
2. to make Th2 cells, you need IL 4
What cells are capable of activating T and B cells?
APCs
- 2 signals are required to activate these cells
What are the steps of T cell activation
- Foreign body is phagocytosed by dendritic cells
2 Forgeign Ag is presented on MHC II and recognized by TCR on T helper cells. Ag is presented on MHC I to cytoxic cells — this is the 1st signal - Costimulatory signal is given by interaction of B7 and CD28 ( signal 2)
- T helper cells activates and produces cytokines
Cytotoxic T cells activates and is able to recognize and kill virus infected cells
How are B cells activated?
- First you need to get helper T cell activated so remember that process (TCR binds to Ag on MHC II, and B7 binds to CD28 for co-stimulation)
- B cell receptor mediated endocytosis, foreign Ag is presented on MHC II and recognized by TCR on T helper cells (signal I)
- CD 40 receptor on B cell binds CD40 ligand on Th cells (signal 2)
- Th cell secretes cytokines that determine Ig class switching of B cell. B cell activates and undergoes class switiching, affinity maturation, and Ab production
What do Th1 cells do?
- secrete IFN-gamma and IL2
2. activated macrophages and cytotoxic T cells
What cytokines inhibit Th1 cells?
by Il 4 and 10 from Th2 cells
What do Th2 cells do?
- secrete Il 4, 5, 10, and 13
2. Recruit eosinophils for parasite defense and promote IgE production by B cells
What cytokines inhibt Th2 cells?
IFN-gamma
Tell me about macrophage-lymphocyte interaction
Activated lymphocytes release IFN-gamma and macrophages release IL1 and TNF alpha stimulating each other
What do helper T cells and cytotoxic T cells have in terms of CD and what receptors do they bind to in terms of MHC?
- Th cells have CD4 bind to MHC II
2. Tc cells have CD8 bind to MHC I
What are the roles of cytotoxic T cells?
- kill virus-infected, neoplastic, and donor graft cells by inducing apoptosis
How do cytotoxic T cells work?
they release cytotoxic granules containing preformed proteins
- perforin - makes holes in membranes
- granzyme - serine protease that activates apoptosis inside target cells
- granulysin - antimicrobial, induces apoptosis
what are regulatory T cells?
help maintain specific immune tolerance by suppressing CD4 and CD8 T cell effector functions
What surface markers do regulatory T cell express?
- CD3, CD4, CD25 (alpha chain of IL 2 receptor)
What cytokines do regulatory T cell produce?
anti-inflammatory cytokines like IL10 and TGF beta
What is the structure of Abs?
- 2 light chains (lambda or kappa)
- 2 heavy chains ( Mu, Delta, Gamma, Alpha, Epsilon)
- Variable part of L and H chains recognize Ags
- Heavy chain contributes to Fc and Fab fractions
- Light chain contributes to Fab fractions
What holds the structure of Abs together?
Disulfide bonds - the exist within the heavy and light chains. They hold the heavy chains together. They hold the heavy and light chains together as well.
What is the role of the Fab portion of the Ab?
- Ag binding fragment
- determines idiotype: unique antigen binding pocket; only 1 antigenic specificity expressed per B cell
What is the role of the Fc portion of the Ab?
- constant chain
- carboxy terminal of Ab
- complement binding at Ch2 (IgG and IgM only)
- carbohydrate side chains
determines isotype of Ab
How is Ab diversity generated?
by random recombination of VJ (light chain) or VDJ (heavy chain) genes
- random combination of heavy chains w/ light chains
- somatic hypermutation (following Ag stimulation)
- Addition of nucleotides to DNA during recombination (see 1st entry in this list) by terminal deoxynucleotidy transferase
- rearrangement begins w/ break in dsDNA at recombination signal sequences (RSS) that flank the VDJ coding regions - RAG 1 and 2 recognize the RSS
What what happens there are mutations in the RAG genes?
inability to initiate VDJ rearrangement and an arrest of B and T cells
What is the normal ratio of lambda to kappa light chains?
2:1
What is the role of IgG
- main Ab in the delayed response to an Ag
- fixes complement and crosses the placenta (provides passive immunity to infant)
- opsonizes bacteria, neutralizes bacterial toxins and viruses
What is the most abundant Ab?
IgG
What is the role of IgA?
- prevents attachment of bacteria and viruses to mucous membranes
- does NOT fix complement
- crosses epithelial cells by transcytosis
- picks up secretory component from epithelial cells before secretion
What are the forms that IgA can be found in?
- in circulation = monomer
- when secreted = dimer
Where can IgA be found?
in secretions (tears, saliva, mucus) and early breast milk (colostrum)
What is the role of IgM?
- produced in the immediate response to an Ag
- Fixes complement but does NOT cross the placenta
- Ag receptor on the surface of B cells
- monomer on B cell or pentamer
Why does IgM exist in a pentamer form>
allow it to efficiently trap free antigens out of tissue while humoral response evolves
What is the role of IgD?
unknown; found on surface of many B cells and in serum
What is the role of IgE?
- binds mast cells and basophils
- cross -links when exposed to allergens, mediating immediate (type I) HSR through release of inflammatory mediators such as histamine
- mediates immunity to worms by activating eosinophils
- lowest concentration in serum
What is thymus independent Ag?
Ag lacking a peptide component
- can’t be presented to MHC to T cells
- stimulates release of Abs and don’t result in immunologic memory
What are examples of thymus independent Ag?
LPS from cell envelope of gram - negative bacteria and polysaccharide capsular ag
What are thymus dependent Ag?
Ags containing a protein component - class switching and immunologic memory occur as a result of direct contact of B cells w/ Th cells
What is the role of complement?
a system of interacting proteins that play a role in innate immunity and inflammation. MAC of complement defends against gram-negative bacteria
How are the various complement pathways activated?
- Classical = IgG or IgM mediated –> C1 mediated to make a C4b2a C3 convertase
- Alternative = microbe surface molecules –> C3 deposition and C3b interacts w/ Bb to make C3bBb C3 converatse. Bb comes from D
- Lectin = mannose of other sugars on microbe surface
What’s the function of the following complement proteins?
- C3b
- C3a, C5a
- C5a
- C5b-9
- opsonization
- anaphylaxis
- neutrophil chemotaxis (LTB4, IL8)
- MAC formation
What are the main opsonins?
C3b and IgG are two primary opsonins in bacterial defense; C3b also helps clear immune complexes
What are the inhibitors of the complement pathway?
- DAF
- C1 esterase inhibitor
* both help prevent complement activation on self cells
What happens when you have a C1 esterase inhibitor deficiency?
hereditary angioedema.
- ACE inhibitors are contraindicated
What happens w/ a C3 deficiency?
severe, recurrent pyogenic sinus and respiratory tract infections. Increased susceptibility to type III HSR rxns esp GN in kidneys due to complex deposition
What happens w/ C5-9 deficiency?
recurrent Neisseria bacteremia
What happens w/ a DAF (GPI anchored enzyme) deficiency?
complement mediated lysis of RBCs and paroxysmal nocturnal hemoglobinuria (PNH)
What are all the cytokines secreted by the macrophage?
IL 1, 6, 8, 12, and TNF alpha
What is the role of IL 1?
- endogenous pyrogen
- causes fever, acute inflammation
- activates endothelium to express adhesion molecules
- induces chemokine secretion to recruit leukocytes
What is the role of IL 6?
- endogenous pyrogen
- also secreted by Th2 cells
- causes fever and stimulates production of acute phase proteins