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