Body's Defense: Physical Barriers

• The body uses multiple barriers to prevent, identify, neutralize, and eliminate invading microorganisms.

Physical Barriers

• Epithelia are a crucial first line of defense that prevents microorganisms from entering the internal environment.
• Epithelial cell layers line important organs and openings, coupled with secretions like saliva and tears, protect permeable membranes.
• Skin, with its epidermis, dermis, hypodermis, and fatty tissue, is a robust physical barrier.
• Production of oils and sweat alters the skin's pH, hindering harmful microorganisms.
• Mucus secretion is vital for capturing and neutralizing microorganisms before infection.
• Goblet cells produce inorganic salts and antimicrobial enzymes like lysozymes.

Clinical Significance of Defense Lines

• Physical barriers comprise the first defense line, contributing to the innate immune response.
• Breaching physical barriers leads to inflammation, triggering macrophages to secrete chemicals like histamine and raise body temperature, inducing fever.
• Inflammation leads to resolution via the adaptive immune response, marked by activated T cells, cytotoxic T cells, B cells, and plasma cells producing pathogen-specific antibodies for long-term memory.

Chemical Barriers

• Chemical and physical barriers often co-function in tissues.
• Enzymes secreted by the body act as chemical barriers.
• Examples of chemical barrier enzymes include lysozymes in tears, pH levels in the gut, and secreted cytokines such as interferons.

Tears as Chemical Barriers

• Lacrimal glands in the upper eyelid secrete soluble IgA, lysozyme, and other enzymes such as lactoferrin and lipocallin to hydrolyze bacterial cell walls and cause cell lysis.
• Corneal epithelium goblet cells produce mucins, soluble PLA2 (sPLA2), and antimicrobial peptides (AMPs) from resident neutrophils.
• Tears are an important innate immune system component.

Stomach Acidity

• The stomach maintains an acidic environment.
• The acidic stomach aids in mineral, protein, and vitamin absorption.
• The acidic stomach environment acts as a defense against harmful bacteria and viruses.

Interferon Production

• Interferon is produced when cells are exposed to a virus or viral components.
• After a virus injects genetic material into a host cell, interferon secretion begins.
• Soluble interferon migrates to neighboring uninfected cells and binds to receptors, activating enzymes that degrade mRNA.
• Degradation of mRNA breaks down the virus and cellular genetic information, destroying the cell and stopping virus from spreading.
• Natural killer (NK) cells produce interferon in response to non-self antigens on cancerous cells and tumors.
• Tumor-infiltrating cells use interferon to activate CD8+ cytotoxic T cells that eliminate cancerous or damaged cells.
• Interferon beta 1b may improve recovery in patients infected with SARS-CoV-2, but more research is needed.

Biological Barriers

• Resident microflora cover the body, forming a biological barrier.
• Around 9 billion microbes inhabit the adult human body.
• Most microbes are beneficial, preventing the overpopulation of pathogenic microbes.
• Resident microflora protects the skin and vital organs and regulates reproduction, mental health, and aging.
• Microbial diversity is influenced by genetics, environment, diet, lifestyle, and hormones.

Explore the body's physical barriers against microorganisms. Epithelia, skin, and mucous membranes prevent pathogen entry. Secretions like oils, sweat, and mucus capture and neutralize threats, forming the first line of innate immune defense.