Chapter 13

Development of the Immune System

  • Focus on the immune system development of Group 8.

The Body's Defence System

  • The immune system comprises various layers of defence to protect against foreign materials, originating from three embryonic germ layers: ectoderm, mesoderm, and endoderm.

Layers of Defence

First Layer: Physical Barriers

  • Includes intact epithelia on both external and internal body surfaces.

  • Derived from ectoderm (skin) and endoderm (gastrointestinal tract).

Second Layer: Innate Immune System

  • Provides rapid response without memory of past infections.

  • Important components include granulocytes from myeloid lineage.

  • Granulocytes develop from hematopoietic stem cells.

Third Layer: Acquired Immune System

  • Also known as adaptive immunity; possesses memory.

  • Dependent on gut microbial colonization.

  • T lymphocytes (T cells) and their unique ability to recognize pathogens.

  • Lymphocyte differentiation occurs in primary lymphoid tissues like the thymus.

Immune Maturation in Newborns

Role of Colostrum

  • Newborns rely on antibodies from colostrum for protection in early life.

  • Their immune systems need to mature postnatally for survival.

Immune Development Timeline

  • Initial immune system development occurs in yolk sac.

  • Stem cells migrate to various organs such as thymus and bone marrow.

Lymphocyte Development

  • Thymus is a primary site for T lymphocyte development.

  • Lymphocytes mature in tissues like lymph nodes and spleen.

  • Differentiation includes large granular lymphocytes (NK cells) and small lymphocytes (T and B cells).

Functions of T and B Lymphocytes

  • T cells mediate cellular immunity; B cells mediate humoral immunity by producing antibodies.

  • Antibodies neutralize foreign antigens and activate complement systems.

T Lymphocyte Maturation

  • Progenitor T lymphocytes undergo proliferation and selection processes in the thymus.

  • Recognition of MHC molecules is crucial for TCR (T Cell Receptor) maturation.

  • Positive selection ensures T cells recognize self-MHC molecules; negative selection eliminates self-reactive T cells.

B Lymphocyte Maturation

  • B lymphocytes mature primarily in bone marrow.

  • B cell receptors (BCRs) can directly recognize antigens.

  • Both positive and negative selections occur to prevent autoimmunity.

  • Mature B cells circulate in blood and secondary lymphatic tissues.

Lymphatic Vascular Development

Types of Development

  • Vasculogenesis: formation of primitive vascular channels.

  • Angiogenesis: growth/remodeling of endothelial cells.

Lymph Nodes and Secondary Lymphoid Organs

  • Role: filter lymph on the way to circulatory system.

  • Centers include Medial Retropharyngeal, Deep Cervical, and Axillary lymph nodes.

Spleen: A Secondary Lymphatic Organ

  • Functions as a blood filter, crucial for the immune system.

  • Contains red pulp (filters blood) and white pulp (contains lymphocytes).

Conclusion

  • Comprehensive understanding of the immune system's development and function through layers of defence, role of various lymphocytes, and their maturation processes in different organs.