Pathos #2: Immunity and Neoplastic Disease — Comprehensive Notes

Innate Immunity

The body's immediate, non-specific defense system present from birth, including physical barriers, cellular defenses (like neutrophils, macrophages, NK cells), and chemical defenses (like the complement system).

Adaptive Immunity

A specific, long-lasting immune response involving T cells and B cells that develops memory for faster responses upon re-exposure to a pathogen.

Phagocytic Cells

Immune cells, such as neutrophils and macrophages, that engulf and destroy pathogens.

Natural Killer (NK) Cells

Specialized immune cells that identify and destroy infected or abnormal host cells, like virus-infected or cancer cells.

Complement System

A group of circulating proteins that promote opsonization and inflammation, leading to pathogen destruction via pathways like classical and alternative, and forming the Membrane Attack Complex (MAC).

Opsonization

The process of marking pathogens with antibodies or complement proteins to enhance their phagocytosis by immune cells.

Humoral Immunity

Antibody-mediated immunity, primarily driven by B cells that differentiate into plasma cells to secrete antibodies, effective against bacteria and bacterial toxins.

Cell-Mediated Immunity

Immunity primarily mediated by T cells, which directly destroy infected cells and regulate other immune responses.

Antibodies (Immunoglobulins)

Proteins secreted by plasma cells that neutralize antigens, mark them for destruction, or act as antigen receptors on B cells.

IgG

The principal antibody in systemic immunity and the classical complement pathway; a monomeric form.

IgM

A pentameric antibody, highly efficacious in early primary responses and efficient at neutralizing fungi; part of the classical pathway.

IgA

A dimeric antibody found in mucosal tissues and breast milk, providing mucosal protection.

IgE

An antibody involved in allergic reactions and defense against parasitic infections, mediating degranulation of mast cells and basophils.

Antigen-Presenting Cells (APCs)

Immune cells (e.g., dendritic cells, macrophages, B cells) that process antigens into fragments and present them on MHC molecules to T cells.

MHC Class I

Major Histocompatibility Complex molecules that present intracellular antigens to CD8+ cytotoxic T cells.

MHC Class II

Major Histocompatibility Complex molecules that present extracellular antigens (captured by APCs) to CD4+ helper T cells.

Cytotoxic T (CD8+) Cells

T cells that identify and destroy infected host cells and abnormal cells (e.g., cancer cells).

Helper T (CD4+) Cells

T cells that regulate the immune response, assisting other immune cells like B cells in their activation and antibody production.

Human Leukocyte Antigen (HLA)

Immune response genes on chromosome 6 that regulate immune cell proliferation and function, influencing disease susceptibility.

Hypersensitivity Reactions

Exaggerated or abnormal immune responses to antigens that can cause tissue damage.

Type I Hypersensitivity

IgE-mediated immediate allergic reactions, such as anaphylaxis, involving histamine release from mast cells/basophils.

Type IV Hypersensitivity

Delayed or cell-mediated hypersensitivity involving sensitized T cells reacting on re-exposure, activating macrophages and causing inflammation (e.g., contact dermatitis).

Autoimmune Diseases

Conditions resulting from a breakdown of immune tolerance, where the immune system attacks self-antigens.

Vaccines

Preparations that prime the immune system to recognize specific pathogens and mount quicker, stronger responses upon future exposure.

Benign Tumors

Localized, well-circumscribed, usually slow-growing non-invasive tumors that do not invade surrounding tissues or metastasize.

Malignant Tumors

Cancerous tumors that invade adjacent tissues and can metastasize to distant organs via blood or lymphatic routes.

Carcinomas

Malignant tumors arising from epithelial tissues, accounting for \~85 ext{ to }90 ext{ percent} of cancers (e.g., skin, colon, breast cancer).

Sarcomas

Malignant tumors arising from connective tissues like bone, muscle, or fat, often metastasizing rapidly.

Leukemias

Cancers of blood cells that proliferate in the bone marrow and circulate in the blood, crowding out normal hematopoietic cells.

Oncogenes

Mutated proto-oncogenes that promote uncontrolled cell growth and division, driving tumorigenesis.

Tumor Suppressor Genes

Genes that normally restrain cell division; loss of function in both alleles can promote malignancy (e.g., APC gene).

DNA Repair Genes

Genes that maintain genome integrity; mutations in these genes increase overall mutation rate and cancer risk.

Angiogenesis

The process by which tumors induce new blood vessel growth to supply nutrients and oxygen, vital for their growth and metastasis.

Dysplasia

Precancerous changes in cells or tissues that may progress to cancer if untreated, characterized by abnormal cell growth.

Tumor Markers

Substances (e.g., CEA, AFP, hCG, PSA) elevated in blood or tissues that aid in cancer detection, diagnosis, and monitoring.

Cancer Staging

A system (Stage 0 to IV) used to describe the extent of cancer spread, from in situ (Stage 0) to distant metastasis (Stage IV), which influences prognosis and treatment decisions.