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Reminders

Reminders. Exam 3- Questions where mistake in key was corrected: 10: answer AB is correct. 17: answer E is correct. Exam out of 98 points instead of 100. The humoral immune response. B cell activation by TI antigens. Weak B cell response No memory B cells No affinity maturation

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Reminders

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  1. Reminders • Exam 3- • Questions where mistake in key was corrected: • 10: answer AB is correct. • 17: answer E is correct. • Exam out of 98 points instead of 100.

  2. The humoral immune response B cell activation by TI antigens

  3. Weak B cell response No memory B cells No affinity maturation Usually no class switching IgM response. There are two types: TI-1 antigens & TI-2 antigens General Characteristics of TI antigens:

  4. TI-1 antigens: • Large antigens with complex structure. • Bacterial LPS

  5. Crosslinking of BCR & alternative receptors can mediate activation. • LBP= LPS Binding Protein

  6. The amount of TI-1 Ag can impact end outcome • Polyclonal Activation • Mitogen activity

  7. TI-2 Antigens • Repetitive carbohydrate/protein epitopes generally on surfaces of microbes. • bacterial capsules or flagella. • Probable mechanism- • extensive crosslinking of BCR & CoReceptor alleviates need for second signal. • Most responding B cells are B1 cells.

  8. Evidence that another cytokine producing cell can augment the response (DC or Mf).

  9. B1 cells: • Arise during fetal development, full function when ~5 years old.

  10. T Dependent Antigen Requires Th2 cell Assistance

  11. Generates strong B cell & humoral immune response. • + affinity maturation & class switching. • Ag are usually soluble proteins.

  12. B cell & T cell recognize the same antigen • Protein antigens attached to a polysaccharide allow T cells to activate polysaccharide specific B cells.

  13. The In Vivo Humoral Immune Response • Chances for lymphocyte recognition of Ag: • 1 in 10,000 – 1 in 1,000,000. • Chances for T & B cell recognition of same Ag: 1 in 108 – 1 in 1012.

  14. cortex paracortex

  15. T cells produce IL-4, B cells proliferate in the foci & develop into lymphoblasts.

  16. The lymphoblasts: • Differentiate into plasma cells: • Th2 cells- produce IL5 & IL6. • Plasma cells predominantly produce IgM. • Travel to cortex & enter a primary follicle (travel with TH cells): • Continue proliferation & become centroblasts. • forms a secondary follicle with germinal centers.

  17. The Germinal Centers • A specialized microenvironment for B cell proliferation & differentiation- • Somatic hypermutation & Affinity maturation • Only lymphoblasts activated via CD40 with CD40L on Th cells in the primary focus form germinal centers! • Appears 1 week following infection. • Cause of LN swelling.

  18. Germinal center is an island of cell division. 90% = B cells 10% = T cells • Centrocytes • Cell division slows • Increase expression of surface IgM & IgD. • Centroblasts • divide every 6-8 hrs. • Decrease expression of surface IgM & IgD.

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