Immunology: MALT and Major Organs

Regional Immunity (MALT)

• MALT is a key component of the immune system, vital for defending mucosal surfaces.
• Mucosal surfaces are large, exposed areas susceptible to pathogens.

Gastrointestinal Tract

• Special challenges include tolerance of food antigens and commensal microbiota, responsiveness to potential pathogens, and an extensive surface area.
• Specialized cells help regulate immune tolerance, and handle a diverse array of microorganisms.

Respiratory System

• The respiratory system faces a constant barrage of inhaled pathogens and innocuous microbes.
• Ciliary movement and mucus production clear particles and microbes.

Cutaneous Immune System

• Large surface area exposed to microbes and pathogens.
• Keratinizing stratified squamous epithelial barrier provides a protective layer.

Major Lymphoid Organs and Tissues

• Primary lymphoid organs include the thymus and bone marrow.
• Secondary lymphoid organs include lymph nodes, spleen, tonsils, adenoids, Peyer's patches, and bronchus-associated lymphoid tissue (BALT).

Mucosal Immune System

• It's a crucial first line of defense against pathogens that enter the body through mucosal surfaces.
• This system consists of secretory IgA, dendritic cells, T cells, and B cells, effectively defending against microbes, viruses, and allergens.
• The total surface area of the mucosal immune system is about 400 m², significantly larger than the skin's.

MALT Regions

• GALT: Gut Associated Lymphoid Tissue
• BALT: Bronchus Associated Lymphoid Tissue
• NALT: Nasal Associated Lymphoid Tissue
• RALT: Reproductive Associated Lymphoid Tissue

GALT (Peyer's Patch)

• GALT (Peyer's Patch) is a critical component in the gut-associated lymphoid tissue, initiating immune responses.
• T cells, B cells, M cells, and dendritic cells are important participants in initiating and coordinating immune responses.

PP Structure

• Peyer's Patch (PP) is principally composed of three functional regions:
• Dome Region
• B Lymphoid Region (Follicular Germinal Centers)
• T Lymphoid Region (Parafollicular Zone)

GALT Structure and Function (Immune Compartments)

• Induction Sites: Peyer's patches, appendix, Mesenteric lymph nodes, other lymph nodes deliver antigen to start immune response.
• Effector Sites: Lamina propria (beneath gut epithelium).
• These sites work in tandem to initiate and carry out mucosal immune responses.

M Cells in the Small Intestine

• M cells are specialized epithelial cells found in the intestinal lining.
• They sample and deliver antigens from the intestinal lumen to the underlying immune system.

Cells in the GALT (Epithelial, γδ T, αβ T)

• Epithelial cells and innate lymphoid cells contribute to mucosal immunity by creating an interface between the gut and external environment.
• γδ T cells play specialized roles in early immune responses and antigen presentation.
• αβ T cells and B cells coordinate the specific adaptive immune response for antigen surveillance.

Innate Immunity in Gastrointestinal Tract

• Intestinal epithelial cells are essential for the innate immune response in the gastrointestinal tract.
• These cells are involved in immune responses, tolerance to commensal organisms, and antigen sampling for the adaptive immune system.
• Mucosal layers prevent pathogens from coming into contact with epithelial cells.

Role of Th1 and Th2 cells

• Th1 and Th2 cells are crucial for producing mucosal IgA, a key antibody for defense in mucosal surfaces.
• These cells play a crucial role in initiating the IgA response.

IgA1 and IgA2 Antibody Producing Cells

• Different mucosal sites have varying proportions of IgA1 and IgA2 producing cells.
• This demonstrates the localized and specific nature of mucosal immune responses.

Lymphocyte Circulation

• Lymphocytes continuously circulate between mucosal tissues, lymphatic vessels, and the bloodstream to maintain immune surveillance.
• This circulation ensures that immune cells are readily available for antigen detection and response.

This quiz covers the Regional Immunity concepts, focusing on MALT, the gastrointestinal tract, the respiratory system, and the cutaneous immune system. It also explores the roles of major lymphoid organs and tissues in immunity. Test your understanding of these crucial components of the immune system.