Immune System

What are the three lines of defense in the immune system?

1st line (physical barriers), 2nd line (innate internal cellular defense), and 3rd line (adaptive immunity).

Where do all immune cells originate?

From hematopoietic stem cells in the red bone marrow.

What are the phagocytic cells of the innate immune system?

Neutrophils, monocytes (macrophages), and dendritic cells.

What is chemotaxis?

Chemical signals attracting circulating leukocytes to infected areas.

What is diapedesis?

A leukocyte exiting blood vessels to enter tissues.

What are non-phagocytic innate immune cells?

Eosinophils, mast cells, basophils, and natural killer cells.

What are Toll-like receptors (TLRs)?

Receptors on innate immune cells that recognize foreign molecular patterns.

What are cytokines?

Chemical signaling molecules used by immune cells for cell-cell communication.

What do interferons do?

Cytokines secreted by infected cells that signal neighboring cells to defend against viruses.

What is the complement system?

Proteins that assemble pores in pathogen membranes, leading to cell lysis.

What triggers the inflammatory response?

Mast cells releasing histamine (causing vasodilation and increased permeability), recruitment of neutrophils/macrophages, and local prostaglandins.

What is an antibody?

A Y-shaped glycoprotein produced by B cells consisting of heavy and light chains, a variable region (binds antigens), and a constant region.

What are the five classes of antibodies?

IgG, IgA, IgM, IgE, and IgD.

What is MHC I?

Glycoproteins found on all nucleated vertebrate cells that present internal protein fragments.

What is MHC II?

Glycoproteins found only on antigen-presenting cells that present external antigens.

What is the humoral response?

Adaptive immune response involving B cells stimulated by extracellular pathogens, producing plasma cells (antibodies) and memory B cells.

What are the mechanisms by which antibodies fight pathogens?

Opsonization, neutralization, agglutination, and enhancing other systems.

What is the cell-mediated response?

Adaptive immune response involving T cells (matured in the thymus) producing cytotoxic T cells, helper T cells, suppressor T cells, and memory T cells.

What is T-cell positive selection?

Occurs in the thymus cortex; T cells that can bind to MHC survive.

What is T-cell negative selection?

Occurs in the thymus medulla; T cells that bind too tightly to self-antigens are eliminated.

What is the difference between active and passive immunity?

Active immunity is acquired after direct exposure to a pathogen (natural or vaccine); passive immunity is acquired from external sources (natural via mother or artificial via serum injection).

What mnemonic recalls the relative abundance of white blood cells?

"Never Let Monkeys Eat Bananas" (Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils).