MICB 212 Chapter 1 Notes

Introduction to the Immune System

-environment is filled with microorganisms that humans encounter everyday

  • bacteria, viruses, fungi, parasites

-some microorganisms can cause disease but most people are healthy most of the time

-humans and other vertebrates protect themselves with a complex array of defensive mechanisms

3 Levels of Defense Against Infection

  1. anatomical and physical barriers

    • intact skin provides a physical barrier

    • mucosal surfaces of gut, respiratory urogenital and conjunctivae surfaces

    • stomach acid, lysozyme and other antimicrobial body secretions

  2. innate immune response (initial internal defense)

    • quick and non-specific

    • involves phagocytosis and activation of complement proteins

    • limits spread of infection

    • often resolves infection

  3. adaptive immune response (last line of defense)

    • slow to respond but specific to particular pathogen

    • involve antibody-mediated responses and cell-mediated responses

Cells of Immune System

2 Major Cell Populations in Blood

  1. erythrocytes/red blood cells (RBCs)

    • carries oxygen to the tissues

  2. leukocytes/white blood cells (WBCs)

    • cells of immune system

-all blood cells arise from hematopoietic stem cells (HSC)

-hematopoietic cells are self-renewing

  • found in bone marrow, umbilical cord, in blood (small amounts)

Leukocytes

-separated into

  • myeloid cells

  • lymphoid cells

Myeloid Cells

  • participate in innate immune response

  • includes

    • monocytes (mature into macrophages)

    • mast cells

    • granulocytes (neutrophils, basophils, eosinophils)

Lymphoid Cells (Lymphocytes)

  • participate in adaptive immune response

  • includes

    • cytotoxic T cells (CTLs)

    • T helper (Th) cells

    • T regulatory (Treg) cells

    • B cells

Dendritic Cells

-link between innate and adaptive response

-important cells for

  • activating T cells

  • initiating adaptive immune response

-dendritic cells derived from lymphoid cells or myeloid cells

  • all cells of blood and immune system derived from common hematopoietic stem cell

Location of Immune System

-distributed throughout the body

-cells of immune system found in

  • blood circulatory system

  • lymphatic circulatory system

    • enables lymphocytes and proteins to move around body

    • lymph fluid similar to blood but lacks RBCs and platelets

    • connects different lymph nodes together

  • lymphoid organs

    • primary lymphoid organs

    • secondary lymphoid organs

-lymphatic circulatory system and blood circulatory system are connected

  • fluids in tissues drain into lymphatic capillaries then into lymph nodes

  • lymphatic fluid returns to blood circulatory system via thoracic duct located near heart

Primary Lymphoid Organs

-sites where lymphocytes develop and mature

  • includes

    • bone marrow

    • thymus

-all hematopoietic cells (blood & immune cells) complete process (developmentation & maturation) in bone marrow

  • except T cells → begins in bone marrow → completes in thymus

Secondary Lymphoid Organs

-sites where mature lymphocytes encounters pathogens/foreign molecules and begins adaptive immune responses

  • includes

    • spleen

    • lymph nodes

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