Summary: Physiology: Specific Cells

Read the summary and the most important questions on Physiology: Specific Cells

• 1 Lecture 18: MHC

• 1.1 Major Histocompatibility Complex

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• What are the molecular differences between Class 1 and Class 2 MHC?

  Class 1: a1, a2, a3, b2 chains
  Class 2: a1, a2, b1, b2 chains
  
  Their peptide binding clefts are different as well

• 1.1.1 Restriction

• What makes transplantation medicine harder?

  1. No two individuals will have the same MHC haplotypes as they are highly polymorphic, makes it harder to make organ transplantation happen as they might not be compatible.
  2. T cells responses can only be initiated by self MHC's epitope presentation, as foreign MHC molecules are potential danger signals
  

• 1.1.2 Diversity

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• What does complexity of haplotypes lead to?

  More complex haplotypes can present a broader array of epitopes, but this also increases the risk of autoimmune disease
  
  Less complex haplotypes has low risk of autoimmune disease, but can only present a limited array of epitopes and are, therefore at greater risk of infectious diseases

• What does inbreeding do in terms of MHC?

  Inbreeding leads to reducing MHC complexity as haplotypes from same families are likely to be similar when compared to non-related individuals from the same species.
  Bottlenecks and artificial selection/breeding can lead to restriction of MHC

• 1.2.1.1 Primary lymphoid tissues vs Secondary lymphoid tissues

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• How do lymph nodes work?

  - Afferent lymphatic vessels: bring lymph (lymphocytes, antigens) into the nodes
  - Efferent lymphatic vessels: allow cells (activated effector cells) to exit the nodes to seek out targets

• What are the germinal centers lymph nodes?

  Germinal centers are in the cortex of lymph nodes; where B cell responses are initiated, also called B cell follicles
  - Dark zone: centroblasts (rapidly dividing B cells), as clonal expansion and somatic hypermutation for antibody and BCR diversity 
  - Light zone: centroycytes (non-dividing B cells), follicular DCs and T follicular helper cells, where antigens bind to FDCs and MHC-II leads to affinity testing of Tfh cells to B cells. Will lead to selection and differentiation to plasma cells or memory B cellshow 
    

• What do peyer's patches do?

  Dendritic cells patrol and sample pathogens or commensal bacteria and take them to peyer's patches for development and maturation of T cells and B cells for maintaining gut microbiota

• Where do primary and secondary immune responses take place?

  The primary immune response to IV injected antigen takes place in the lymph nodes or spleen, the antibodies produced during a secondary response are mainly generated in the bone marrow

• 1.2.1.2 T cell activation

• How do activating T follicular helper cells lead to B cell activation?

  Activated T follicular helper cells (via MHC-II and follicular DC) drive B cell activation by providing essential, direct help within lymph node follicles, primarily through their CD40L binding to CD40 on B cells, along with the secretion of cytokines like IL-21 and IL-4. This interaction triggers B cell proliferation, differentiation into plasma or memory cells, isotype switching, and somatic hypermutation

• 1.2.1.3 Trafficking of lymphocytes

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• How do lymphocytes travel?

  Lymphocytes travel throughout the body via blood vessels and lymph vessels.