The Immune and Lymphatic Systems

The Immune System

• The immune system is a complex network of cells, tissues, and organs
• It works to protect the body from harmful invaders like bacteria, viruses, and fungi
• There are two major types of immunity: innate and adaptive

The Lymphatic System

• Consists of lymphatic capillaries, vessels, lymph nodes, and lymphatic organs
• Drains excess fluid from tissues back into circulation
• Filters lymph to remove pathogens and foreign material
• Part of the immune system

Innate Immunity

• The body's first line of defense against pathogens

• Rapid response to a broad range of microbes

• Includes external defenses like skin and mucous membranes, and internal defenses like phagocytic cells, antimicrobial proteins, and the inflammatory response

• Skin is the body's largest organ and is a physical barrier

• Skin contains chemical weapons like oil and sweat glands, lysozyme, and normal flora that prevent pathogen growth

• The digestive, respiratory, and urogenital tracts are other potential infection routes

• The lining of these tracts contain cells that secrete mucus and have other mechanisms to trap microbes

• Three other potential infection routes are the digestive tract with mucus, saliva, lysozyme, and acidic stomach contents

• The respiratory tract with ciliary action

• The urogenital tract with acidic urine

• Nonspecific defensive molecules include interferon, defensins, and cathelicidin

• Interferon is a signaling protein against pathogens

• Defensins are proteins against bacteria, fungi, and viruses

• Cathelicidin is a mammalian innate immune protein against bacteria

• Inflammatory response involves several body systems

• Chemicals from injured cells, such as histamine and prostaglandins, cause nearby blood vessels to dilate

• Increase in permeability promotes phagocyte accumulation

• Hallmark signs of inflammation include redness, warmth, swelling (edema), pain, and potential loss of function

• Inflammation is accompanied by an acute phase response, one manifestation is fever

• Macrophages release interleukin-1 protein to raise body temperature

• Promotes the activity of phagocytes, while impeding microbial growth

Adaptive Immunity

• Slower but highly specific response to pathogens

• Characterized by specificity, diversity, memory, and the ability to distinguish self from nonself

• The adaptive immune system begins with the recognition of antigens; components of microorganisms or proteins that provoke a specific immune response

• Antigens found on red blood cells, or transplanted tissue cells stimulate a unique immune response.

• Includes B lymphocytes (B cells) and T lymphocytes (T cells)

• B cells are produced and continue development in bone marrow and respond to antigens by secreting antibodies; participating in humoral immunity

• T cells develop in the thymus and regulate other immune cells or directly attack cells carrying specific antigens; participating in cell-mediated immunity

• Humoral immunity begins when naive B cells are activated after meeting antigens

• B cells are activated after their surface immunoglobulins bind to the antigens

• Activation leads to clone expansion and differentiation into plasma and memory cells

• Immune responses recognize antigens by having memory; responding faster and with greater effectiveness after an initial encounter

• The first encounter with a foreign antigen is called the primary immune response

• The second encounter is the secondary immune response which is characterized by a large clone of memory cells detecting the antigen immediately

• The secondary response is faster and more effective due to large clone of memory cells

• The two main types of lymphocytes have different receptors for binding to antigens; B cell receptor is an immunoglobulin (Ig) or antibodies; T cell receptor is on the surface of T cells

• B and T cells can both recognize antigens for producing immune responses; B cells release antibodies

• T cells recognize and directly attack cells with specific antigens