Day 8 · B Cells and Cancer Immunology

Session 1: Prof. Anjali

B-Cells

Unique Function of B-Cells:
- Synthesis of immunoglobulins (Not all immunoglobulins are antibodies).
Innate Immunity Overview:
- Innate immunity includes humoral and cell-mediated responses.
- T and B cells are components of the acquired immune system.
- B cells contribute to humoral immunity by producing immunoglobulins.

Immunoglobulins

Distribution of Immunoglobulins:
- Found on B cell surfaces as antigen receptors.
- Present in blood, mucous membranes, body fluids (tears, saliva, secretions of GI/GU tracts, respiratory systems).
- Attached to Fc receptors.
- Act as cell surface antigen receptors (anchored to cell membrane) and as secreted antibodies.
Identification of B Cells:
- Identified by surface immunoglobulins (1 x 10^5).
- Expression of markers like B220, CD19, MHC Class II, complement receptors, and FC receptors for IgG.
- B1 Cells also express CD5 in addition to BCR and CD19.

Sites of B Cell Synthesis

Pre and Post-Birth Locations:
- Before birth: Yolk sac, fetal liver, fetal bone marrow.
- After birth: Mainly in bone marrow.
B Cell Development Pathways:
- Two distinct pathways: antigen-independent and antigen-dependent.
- Stromal cells support B cell development by providing stem cell factors and cell division molecules.
- Sequential stages: Pro B cells → Pre B cells → Immature B cells → Mature B cells.
- Antigen-independent phase: Leads to the generation of IgM-bearing immature B cells and IgM+IgD-bearing mature B cells.
- Antigen-dependent phase: Triggered by antigens, leading to clonal expansion, memory cell formation, plasma cell differentiation.

Lymphocyte Recirculation Routes

Lymphocyte Movement:
- Lymphocytes recirculate through blood and lymph to various lymphoid organs multiple times a day.
- Percentage of lymphocytes exiting blood to different sites (spleen, lymph nodes, barrier tissues).

Epitopes and Antibody Recognition

Epitopes/ Antigenic Determinants:
- Epitope: Specific part of an antigen recognized by antibodies, B cells, or T cells.
- Characteristics of epitopes: Hydrophilic, surface-exposed, flexible.
- Core epitope: 5-6 residues with surrounding residues involved in complementarity.
- Antibody idiotope (15-22 amino acids) interacts with 15-22 amino acids of antigen.

Diversity in Antibody Specifications

Immunoglobulin Gene Production:
- Vast diversity due to highly variable regions at the NH2 terminus and constant regions in 2/3rd of the molecule.
- Presence of multiple isotypes with the same antigenic specificities.
- Involvement of multiple genes in immunoglobulin chain formation.
Discovery of Immunoglobulin Genes:
- In 1976, Nobel Prize awarded for identifying which gene codes for specific parts of the antibody chain.

These topics covered the unique functions of B cells, the synthesis and distribution of immunoglobulins, B cell identification markers, stages of B cell development, lymphocyte recirculation, epitopes and antibody recognition, and the diversity of antibody specifications.

Feel free to request further elaboration or additions!