Ch. 1. Introduction to the Immune System

Question 1

Immune system

Answer 1

The molecules, cells, tissues, and organs that collectively function to provide immunity, or protection, against foreign pathogens and cancers.

Question 2

Immune response

Answer 2

A collective and coordinated response tot he introduction of foreign substances in an individual mediated by the cells and molecules of the immune system.

Question 3

Lymphoid cells

Answer 3

Include B cells, T cells, innate lymphoid cells, and natural killer cells, all derived from a common lymphoid progenitor.

Question 4

Myeloid cells

Answer 4

Cells derived from the myeloid lineage of hematopoietic precursors, including granulocytes, monocytes, and dendritic cells.

Myeloid cells are distinct from lymphoid cells, which include B cells, T cells, innate lymphoid cells, and natural killer cells, all derived from a common lymphoid progenitor.

Question 5

Leukocytes

Answer 5

White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells. Leukocytes are found throughout the body, including the blood and lymphatic system.[1]

Question 6

Humoral immunity

Answer 6

The type of adaptive immune response mediated by antibodies produced by B lymphocytes. Humoral immunity is the principal defense mechanism against extracellular microbes and their toxins.

Question 7

Cell-mediated immunity (CMI)

Answer 7

The form of adaptive immunity that is mediated by T lymphocytes and serves as the defense mechanism against various types of microbes that are taken up by phagocytes or infect non-phagocytic cells.

Cell-mediated immune responses include CD4+ T cell-mediated activation of of phagocytes and CD8+ CTL-mediated killing of infected cells.

Question 8

Active immunity

Answer 8

The form of adaptive immunity that is induced by exposure to a foreign antigen and activation of lymphocytes and in which the immunized individual plays an active role in responding to the antigen.

This type contrasts with passive immunity, in which an individual receives antibodies or lymphocytes from another individual who was previously immunized.

Question 9

Passive immunity

Answer 9

The form of immunity to an antigen that is established in one individual by transfer of antibodies or lymphocytes from another individual who is immune to that antigen.

The recipient of such a transfer can become immune to the antigen without ever having been exposed to or having responded to the antigen.

Examples of passive immunity are the transfer of human sera containing antibodies specific for certain microbial toxins or snake venom to a previously unimmunized individual, as well as maternal IgG that is delivered int he fetus through the placenta, which protects babies from infections for about six months.

Question 10

Innate immunity

Answer 10

Protection against infection that relies on mechanisms that exist before infection, are capable of a rapid response to microbes, and react in essentially the same way to repeated infections.

The innate immune system includes epithelial barriers, phagocytic cells (neutrophils, macrophages), NK cells, the complement system, and cytokines, largely made by dendritic cells and mononuclear phagocytes.

Innate immune reactions also eliminate damaged and necrotic host tissues.

Question 11

Adaptive immunity

Answer 11

The for of immunity that is mediated by lymphocytes and stimulated by exposure to foreign antigens.

In contrast to innate immunity, adaptive immunity is characterized by exquisite specificity for distinct molecules and by long-term memory, which is the ability to respond more vigorously to repeated exposure to the same microbe.

Adaptive immunity is also called specific immunity or acquired immunity.

Question 12

Primary immune response

Answer 12

An adaptive immune response that occurs after the first exposure of an individual to a foreign antigen.

Primary responses are characterized by relatively slow kinetics and small magnitude compared with responses after a second or subsequent exposure.

Question 13

Secondary immune response

Answer 13

An adaptive immune response that occurs on second exposure to an antigen.

A secondary response is characterized by more rapid kinetics and greater magnitude relative to the primary immune response, which occurs on first exposure.

Question 14

Generative (central) lymphoid organs

Answer 14

An organ in which lymphocytes develop from immature precursors. The bond marrow and thymus are the major generative lymphoid organs in which B cells and T cells develop, respectively.

Question 15

Peripheral (secondary) lymphoid organs and tissues

Answer 15

Organized collections of lymphocytes and accessory cells, including the spleen, lymph nodes, and mucosa-associated lymphoid tissues, in which adaptive immune responses are initiated.

Synonymous with secondary lymphoid organs.

Question 16

Naive lymphocyte

Answer 16

A mature B or T lymphocyte that has not previously encountered antigen.

When naive lymphocytes are stimulated by antigen, they differentiate into effector lymphocytes, such as antibody-secreting B cells, cytokine-producing helper T cells, and CTLs capable of killing target cells.

Naive lymphocytes have surface markers and recirculation patterns that are distinct from those of previously activated lymphocytes. (“Naive” also refers to an unimmunized individual.)

Question 17

Effector cells

Answer 17

The cells that perform effector functions during an immune response, such as secreting cytokines (e.g., helper T cells), killing microbes (e.g., macrophages), killing microbe-infected host cells (e.g., CTLs), or secreting antibodies (e.g., differentiated B cells).

Question 18

Cytokines

Answer 18

Proteins that are produced and secreted by many different cell types, and mediate inflammatory and immune reactions.

Cytokines are principal mediators of communication between cells of the immune system.

Question 19

Memory lymphocytes

Answer 19

Memory B and T cells are produced by antigen stimulation of naive lymphocytes and survive in a functional quiescent state for may years after the antigen is eliminated.

Memory lymphocytes mediate rapid and enhanced (i.e., memory or recall) responses to second and subsequent exposure to antigens.

Question 20

Lymph node

Answer 20

Small nodular, encapsulated lymphocyte-rich organs situation along lymphatic channels throughout the body where adaptive immune responses to lymph-borne antigens are initiated.

Lymph nodes, which are secondary or peripheral lymphoid organs, have a specialized anatomic architecture that regulates the interaction of B cells, T cells, dendritic cells, macrophages, and antigens to maximize the induction of protective immune responses.

Lymph nodes also perform a filtering function, trapping microorganisms and other potentially harmful constituents in tissue fluids and preventing them from draining via the lymph in the blood.

Question 21

Lymph

Answer 21

Lymph (from Latin, lympha meaning “water”[1]) is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to the central circulation. Interstitial fluid – the fluid which is between the cells in all body tissues[2] – enters the lymph capillaries. This lymphatic fluid is then transported via progressively larger lymphatic vessels through lymph nodes, where substances are removed by tissue lymphocytes and circulating lymphocytes are added to the fluid, before emptying ultimately into the right or the left subclavian vein, where it mixes with central venous blood.

Question 22

Spleen

Answer 22

A secondary lymphoid organ in the left upper quadrant of the abdomen. The spleen is. the major site of adaptive immune responses to blood-borne antigens.

The red pulp of the spleen is composed of blood-filled vascular sinusoids lined by active phagocytes that ingest opsonized antigens and damaged red blood cells.

The white pulp of the spleen contains lymphocytes and lymphoid follicles where B cells are activated.

Question 23

Cutaneous immune system

Answer 23

The components of the innate and adaptive immune systems found in the skin that function together in a specialized way to detect and respond to pathogens on or in the skin and to maintain homeostasis with commensal microbes

Components of the cutaneous immune system include keratinocytes, Langerhans cells, dermal dendritic cells, intraepithelial lymphocytes, and dermal lymphocytes.

Question 24

Mucosal immune system

Answer 24

A part of the immune system that responds to and protects against microbes that enter the body through mucosal surfaces, such as the gastrointestinal and respiratory tracts, but also maintains tolerance to commensal organisms that live on the outside of the mucosal epithelium.

The mucosal immune system is composed of organized mucosa-associated lymphoid tissues, such as Peyer patches, as well as diffusely distributed cells within the lamina propria.

Question 25

Parenchyma

Answer 25

The parenchyma is the functional parts of an organ, or of a structure such as a tumour in the body. This is in contrast to the stroma, which refers to the structural tissue of organs or of structures, namely, the connective tissues.

Question 26

Stroma

Answer 26

Stroma (from Greek στρῶμα ‘layer, bed, bed covering’) is the part of a tissue or organ with a structural or connective role. It is made up of all the parts without specific functions of the organ - for example, connective tissue, blood vessels, ducts, etc. The other part, the parenchyma, consists of the cells that perform the function of the tissue or organ.[1]

Question 27

Immunity

Answer 27

Protection against disease, usually infectious disease, mediated by the cells and tissues that are collectively called the immune system.

In a broader sense, immunity refers to the ability to respond to foreign substances, including microbes and non-infectious molecules.

Question 28

Lymphatic system

Answer 28

A system of vessels throughout the body that collects tissue fluid call lymph, originally derived from the blood, and returns it, through the thoracic duct, to the circulation.

Lymph nodes are interspersed along these vessels and trap and retain antigens present in the lymph.