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31 Cards in this Set

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What is the time frame of immunoimmaturity for a child?
In utero and neonatal (3 months).
What types of T cells are produced in the thymus?
Non-self reactive gamma-delta T cells, alpha-beta CD3,4 T cells, CD3,8 T cells, and CD4,25 T reg cells. This is the T-cell repertoire that leaves the thymus.
What is the objective of post-thymic T cells?
To fill in the peripheral lymphoid tissue as the fetus grows.
What does the presence of TREC indicate?
Recent emigration of a T-cell from the thymus.
What cytokine is responsible for the immature T-cell/thymocytes populating the periphery?
IL-7.
What does it mean that a T-cell is naive?
It has never had an antigenic encounter.
What is the phenotype of a naive T-cell?
CD3,4 RA+(RO-).
What is the circulation pathway of a naive T-cell?
Constantly recycles through lymphoid tissue looking for specific antigen to encounter.
In utero and in neonates, what will naive Th0 cells tend to develop into and why?
Th2 response because Th0 cells are insensitive to IL-12 and INF-gamma (directors toward Th1 response), while also secreting TGF-beta and IL-10 (downregulators of Th1), even if there's no antigen present.
What is the primary arm of the in utero and neonatal immune system?
Innate immune system.
Which Ab isotype is produced by the Th2 biased response of the fetus in the case of an intrauterine infection?
IgM because B-cells are poorly responsive to isotype differentiating cytokine signals.
How can the IgM response be used to detect infections in utero?
By analyzing the specificity of the IgM produced, HIV, syphilis, rubella, and other viruses may be detected.
Immediately after birth, what is the primary arm of the immune response responsible for fighting infection?
Innate immune system.
Why is there a blunted Th1 response/Th2 bias in neonatal infants?
Because Th0 cells are poorly responsive to IL-12 and INF-gamma, and the secretion of IL-10 and TGF-beta suppress Th1 and shift the bias toward Th2.
When will the blunted Th1 response normalize, and what will influence this?
At 3-6 months, and exposure to strong Th1 antigens will aid this process.
What Ab protects the infant before it can synthesize its own Ab's?
Maternal IgG.
How does premature birth affect the immune system?
Increases susceptibility to infection because Ig synthesis is delayed.
When should vaccines be administered to a neonate?
After the first three months, or whenever the neonate begins to produce its own Ab's.
Describe the pattern of IgG, IgA, and IgE synthesis in a developing child.
IgG and IgE develop in children, but IgA is not fully synthesized until adulthood.
When does the thymus begin to lose function?
At the onset of puberty, the thymus begins serious involution.
Why is the T-cell repertoire not affected by thymic involution?
Because the entire repertoire is developed in utero.
What is the phenotype of antigen experienced, peripheral T-cells?
CD45(RA-)RO+.
What is the phenotype of naive T-cells?
CD45RA.
Describe traffic pattern differences between experienced and naive T-cells?
Naive T-cells continue in recycling patterns through secondary lymphoid tissue looking for antigen, while experienced T-cells go directly for the antigen.
What is immunosenescence?
Decline in immune system function.
Describe the 5 characteristics of the decline in T-cell function during immunosenescence.
1) Decrease in thymic output of T-cells (both CD4 and CD8)
2) Increase in memory T-cells
3) Decrease in naive T-cells, which is a decreased ability to respond to new antigens.
4) Decreased responsiveness to INF-gamma and IL-2 (Th1 response).
5) Decreased function of CD4,25 T-reg function.
Describe the 3 characteristics of the decline in B-cell function during immunosenescence.
1) Increase in non-organ specific auto-Ab's.
2) Increase in serum Ab concentrations.
3) Strong tendency toward the Th2 response, regardless of the stimulus.
Describe what happens to NK cell functionality during immunosenescence.
NK cells lose their ability to kill targets and respond to IL-2. Their total number increases, however, so total function is relatively unchanged.
Describe the decline of the innate immune system during immunosenescence.
The innate system remains intact throughout life.
Describe 3 clinical implications of aging/immunosenescence.
1) Increased prevalence of autoimmune disease as T-reg function deteriorates.
2) Decreasing ability to resist pathogens and increased incidence of cancer resulting in more pneumonia and urinary tract infection.
3) Increase of tumors due to the loss of ability to kill mutant cells.
How might CD4,25 T-reg cells be manipulated by tumors?
Block killing mechanisms of CD8 and NK cells. Also block B-Cell production of Ab's, so Fc and Complement systems can't be activated because no Ab will be bound to Ag.