Chapter 7: Humoral Immunity Flashcards
Difference between IgM on surface of B cell and secreted IgM?
IgM on surface of B cell is a monomer; secreted IgM is a pentamer (highest avidity)
How is the pentamer version of IgM held together?
By J chain synthesized by the cell
Because IgM is incapable of binding to Fc receptors, what are some major disadvantages?
- cannot act as an opsonin or;
- cannot act as a mediator of anti-body dependent cell-mediated cytotoxicity (ADCC)
Hyper IgM syndrome inheritance pattern?
X linked most commonly; can be acquired
Describe the Ig levels in those with Hyper IgM syndrome?
IgG, IgA, and IgE are low
IgM elevated
In addition to high numbers of IgM secreting plasma cells in those with X-linked hyper-IgM syndrome; what are there autoantibodies to found in the blood?
neutrophils, platelets, and red blood cells
What are some symptoms of X-linked hyper IgM syndrome?
- patients fail to make germinal centers during a humoral immune response
- children with this condition suffer recurrent respiratory infections, especially those caused by Pneumocystis jirovecii
What is the defect in hyper-IgM syndrome?
gene encoding the CD 40L, which maps to the X chromosome.
this causes failure of co-stimulatory signal needed for B cell response to T dependent ag. So only IgM is made
What are the 4 sub-isotypes of IgG?
IgG1, IgG2, IgG3, and IgG4
What are the major characteristics of IgG?
- activates complement
- acts as an opsonin, enhancing phagocytosis
- neutralizes pathogen and toxins
- mediates ADCC
- can cross the placenta via receptor mediated transport
Where is IgA commonly produced?
in the submucosa more than in lymph or spleen
Is IgA secreted as a monomer or dimer?
dimer
What are the major functions of IgA?
- major protective defensed of the mucosal surfaces of the body
- Any pathogen that infects the mucosa will induce IgA production by secretion of TGF-B by infected cells and to lesser extent IL-5
- Functions as a neutralizing ab by inhibiting the binding of toxins or pathogens to the mucosa of the digestive, respiratory, and urogenital systems (sole function)
What are the 2 isotypes IgA forms?
IgA1 and IgA2
Can IgA activate complement?
no
Be able to reproduce the biologic functions of ab isotypes? (Which ones can activate complement classical pathway, neutralization, opsonization, ADCC, placental transport, Naive B-cell ag receptor, memory B cell antigen receptor (one only), trigger mast cell granule release)
Reproduce chart
