Immune System Overview

Immune System Overview

• The immune system is a collection of cells, tissues, organs, and molecules that protect against microorganisms, microbial toxins, and tumor cells.
• Lymphoid tissue and organs are divided into central (primary) and peripheral (secondary).

Central Lymphoid Organs

• Bone Marrow: Located within the central cavity of all bones, responsible for blood cell production (hematopoiesis) and development of myeloid and lymphoid cells.

• Thymus Gland: A small gland behind the sternum, facilitating the development and proliferation of T lymphocytes (T cells), differentiating them into cytotoxic or helper T cells.

Peripheral Lymphoid Organs

• Lymph Nodes: Filter lymph, crucial for immune responses.

• Spleen: Filters blood, involved in immune responses to blood-borne pathogens.

• Mucosa-associated lymphoid tissues (MALT): Including tonsils, adenoids, Peyer's patches, and appendix, these tissues are crucial for defending mucosal surfaces.

Immune System Molecules

• Antibodies (immunoglobulins): Proteins produced by B lymphocytes (plasma cells) that specifically target antigens.

• Lymphokines: Cytokines secreted by T lymphocytes, influencing immune responses through signaling between immune cells.

Immune System Cells

Lymphocytes

• B lymphocytes: Produced and mature in the bone marrow, expressing unique antigen-binding receptors (B cell receptors). Upon antigen exposure and cytokine stimulation, most B cells become plasma cells, which produce antibodies. Some become memory B cells for future encounters.

• T lymphocytes: Produced in bone marrow but mature in the thymus, not producing antibodies. They recognize antigens through cell surface MHC receptors.

• Cytotoxic T cells (CD8+): Recognize antigens presented on MHC I molecules, primarily on virus-infected cells and kill them.

• Helper T cells (CD4+): Crucial for both humoral and cellular immune responses. Recognize antigens presented on MHC II molecules and secrete cytokines to activate B cells and other immune cells.

• Two major types:

• Th1 cells: Produce IFN-γ to activate cytotoxic T cells.

• Th2 cells: Produce IL-4 and IL-5 to activate B cells.

• Regulatory T cells (Treg): Suppress immune responses to prevent overactivity.

• Memory T cells: Recognize antigens from previous encounters, initiating rapid responses upon re-exposure.

Other Cells

• Natural Killer (NK) cells: Large granular lymphocytes capable of killing virus-infected cells or tumor cells without prior sensitization. NK cell activity depends on a balance between activating and inhibitory signals.

• Granulocytes (e.g., neutrophils): First responders to infections, possessing bactericidal activity. Neutrophils accumulate at sites of inflammation and form pus. Eosinophils are involved in parasitic infections, Basophils are involved in allergic reactions.

• Monocytes/Macrophages: Migrate into tissues and differentiate into macrophages, performing phagocytosis and presenting antigens to T cells, essential for initiating specific immune responses.

• Dendritic Cells: Phagocytose antigens and present them to T lymphocytes, facilitating the initiation of adaptive immunity, located in tissues and lymphatic areas.

• Antigen-presenting cells: Macrophages, Dendritic cells, and B cells are crucial for initiating adaptive immunity by capturing, processing, and presenting antigens to T cells.

Explore the complex structure and function of the immune system, focusing on both central and peripheral lymphoid organs. This quiz covers essential topics such as bone marrow, thymus gland, lymph nodes, and the spleen. Test your knowledge on how these components work together to defend the body against pathogens.