Lines Of Defense

Lines Of Defense

• Pathogen needs to gain entry, colonization, evade defenses, reproduction, and exit.
• The body defends itself against foreign invaders with three lines of defense: natural barriers, innate immunity, and adaptive immunity.

Natural Barriers

• Natural barriers are the body's first line of defense.
• They provide an immediate surface response, limit entry, colonization, and growth.
• Natural barriers include skin, mucus, acid, and microflora, as they are nonspecific, providing no recognition.

Innate Immunity

• Innate immunity is the second line of defense.
• Provides a systemic, circulating, and quick response to eliminate microbes and limit their spread.
• Activates adaptive response.
• Innate immunity recognizes PAMPs and includes inflammation, fever, and phagocytosis.

Adaptive Immunity

• Adaptive immunity is the third line of defense.
• It is systemic and circulating, but has a slow response.
• Works to eliminate microbes and resolve infection.
• Enhances barriers and innate responses.
• It is specific, recognizing antigens, and includes antibodies and T cells.
• Memory response is faster following subsequent exposures.

Immune System

• The immune system provides systemic defenses through surveillance, recognition, and elimination.
• Leukocytes circulate and search for pathogens or infections.
• Leukocytes have receptors to recognize harmful molecules, such as PAMPs, and nonself antigens.
• Effector leukocytes attack and destroy harmful, nonself microbes.

Circulation

• The circulatory system includes the cardiovascular and lymphatic systems.

Hematopoiesis

• All blood cells are produced from stem cells in red bone marrow.
• Erythrocytes (RBCs) transport blood gases.
• Thrombocytes (platelets) limit blood loss during injury.
• Leukocytes (WBCs) fight infection.
• Hematopoietic stem cells differentiate into megakaryocytes, leukocytes, erythrocytes, and thrombocytes.
• Leukocytes are either granulocytes or agranulocytes.

Leukocytes

• Granulocytes have a lobed nucleus, large cytoplasmic granules, and are part of the innate immune response
• Granulocytes: neutrophils, basophils, and eosinophils.
• Agranulocytes have a rounded nucleus, small granules, and are part of the innate or adaptive immune response.
• Agranulocytes: monocytes (innate) and lymphocytes (adaptive).

Neutrophils

• Neutrophils have a polymorphic nucleus (PMN).
• Most abundant WBC in circulation.
• Early responders to inflammation.
• Leave the blood to enter tissues and eliminate microbes by phagocytosis.
• Have digestive enzymes and toxic chemicals.

Eosinophils

• Eosinophils attack large eukaryotic parasites by attaching to them and producing toxic chemicals to destroy them.

Basophils

• Basophils circulate in very low numbers
• Release chemical mediators of inflammation such as histamine.

Mast Cells

• Mast cells are similar to basophils but play a more important role; they are more abundant and localized to tissues.

Monocytes

• Monocytes are secondary responders to inflammation.
• They leave the blood and become macrophages in tissues, performing phagocytosis.
• Macrophages and dendritic cells (DC) are tissue-resident phagocytes, that present antigens and activate T cell responses.

Lymphocytes

• Lymphocytes are involved in adaptive immunity.
• Consist of 20-35% of circulating leukocytes and 10% of body cells in lymphoid and connective tissues.
• Types of lymphocytes: B cells, plasma cells, helper T cells, cytotoxic T cells, and natural killer (NK) cells, part of the innate immunity.