Host Resistance Overview Quiz

Innate Host Resistance

• Innate host resistance comprises physical and chemical barriers, as well as cellular and molecular responses that provide immediate defense against pathogens.
• It is the first line of defense against microbial invasion and is a vital component of the immune system.

Immune System Overview

• The immune system is composed of distributed cells, tissues, and organs that recognize and respond to foreign substances or microbes.
• Immunity refers to the ability of the host to resist a particular disease or infection.

Immunity and Nonspecific Immune Response

• Nonspecific immune response, also known as innate immunity, acts as the first line of defense against microbes and foreign materials.
• It lacks immunological memory and does not differentiate between pathogens.
• Specific immune response, also known as acquired or adaptive immunity, provides resistance to specific foreign agents and has "memory" that increases effectiveness with repeated exposure.

Antigens and Immune Responses

• Antigens are recognized as foreign and invoke immune responses, ultimately resulting in B cell activation and antibody production.
• Antibodies bind to specific antigens, inactivating or eliminating them, and other immune cells become activated.

White Blood Cells of Innate and Adaptive Immunity

• White blood cells (WBCs) play a major role in both innate and adaptive immune responses.
• Some WBCs mature prior to leaving the bone marrow and respond to all antigens as part of the innate immune system.
• Other WBCs mature after leaving the bone marrow and become part of the adaptive immune response, responding to specific antigens.

Physical and Mechanical Barrier Defenses of Innate Resistance

• Physical barriers, such as skin and mucous membranes, provide a first line of defense against microbial invasion.
• These barriers are impacted by factors like nutrition, physiology, fever, age, and genetics, as well as personal hygiene, socioeconomic status, and living conditions.

Skin as a Physical Barrier

• Skin is a strong mechanical barrier to microbial invasion due to the production of keratin by keratinocytes in the outer layer.
• The skin environment is inhospitable to microbes, with features like pH, NaCl concentration, and periodic drying.

Mucous Membranes

• Mucous membranes form a protective covering that resists penetration and traps many microbes.
• They are bathed in antimicrobial secretions containing substances like lysozyme, lactoferrin, and lactoperoxidase.

Respiratory System

• Turbulent air flow in the respiratory system deposits microbes onto mucosal surfaces, which are then trapped by mucous secretions.
• The mucociliary blanket transports trapped microbes away from the lungs, and they are expelled through coughing or sneezing.

Gastrointestinal Tract

• The stomach contains gastric acid, while the intestines shed columnar epithelial cells, produce pancreatic enzymes, and contain normal microbiota.
• Other defense mechanisms in the gut include secretory IgA, bile, and intestinal enzymes.

Genitourinary Tract

• The genitourinary tract has an unfavorable environment for foreign microbes due to low pH, urea, and other toxic metabolic end products.
• The vagina has a low pH and contains lactobacilli, and the male urethra provides a distance barrier.

The Eye

• The eye is protected by a mucus-secreting epithelial membrane, with mechanisms like flushing with tears, lysozyme, lactoferrin, and secretory IgA in tears.

Chemical Mediators in Innate Resistance

• Inflammation is a nonspecific response to tissue injury or cell death, characterized by redness, warmth, pain, swelling, and altered function.
• Acute inflammation involves the release of inflammatory mediators, margination, diapedesis, and extravasion.
• Chronic inflammation is a slow process involving the formation of new connective tissue, causing permanent tissue damage.

Complement System

• The complement system is composed of over 30 serum proteins that augment the antibacterial activity of antibody.
• It has three major activities: defending against bacterial infections, bridging innate and adaptive immunity, and disposing of wastes.

Cytokines

• Cytokines are soluble proteins or glycoproteins released by one cell population that act as intercellular mediators or signaling molecules.
• They can be classified into three groups based on function: regulators of innate resistance mechanisms, regulators of adaptive immunity, and stimulators of hematopoiesis.

Acute Phase Proteins

• Acute phase proteins are produced in response to bacterial infection, leading to the release of cytokines, liver stimulation, and acute phase protein production.
• Examples include C-reactive protein (CRP), mannan-binding lectin (MBL), surfactant proteins A (SP-A) and D (Sp-D), which can bind bacterial surfaces and act as opsonins.