Host Defense Mechanisms and Pathogen Evasion

The 3 Arms of Host Defense are Innate Immunity, Adaptive Immunity, and Passive Immunity. Innate immunity is the body's first line of defense against pathogens, while adaptive immunity provides a specific response to pathogens. Passive immunity is the transfer of antibodies from one individual to another.

Innate immunity and adaptive immunity are the two main branches of nonspecific defense mechanisms. Antibodies and antigens, T cells and B cells, and inflammation and fever are more specific components of the immune system.

Physical/chemical exclusion barriers are the body's defense mechanisms that prevent entry of pathogens or harmful substances into the body. Skin and mucous membranes, such as those in the nostrils and lungs, are examples of these barriers.

The correct answer explains that the tight junctions between skin cells leave very little room for pathogens to penetrate the skin, making it an effective exclusion barrier.

Desquamation refers to the natural process of dead skin cells being shed from the surface of the skin to allow for the removal of pathogens attached to the outer layer.

Keratin is a tough fibrous protein that forms the structure of hair, nails, and the outer layer of the skin. It is highly resistant to pathogens and provides protection to the body.

Sebum is a natural oily substance produced by the sebaceous glands in the skin. It helps keep the skin and hair lubricated and acts as a barrier against microbes.

SALT in the context of the question refers to Skin-associated lymphoid tissue, which is an important component of the immune system located in the skin.

Mucin acts as an effective exclusion barrier due to its thick layer, containing lysozyme and lactoferrin that prevent pathogens from reaching the epithelial layer and obtaining iron for their enzymatic activity.

The mucociliary escalator is a vital defense mechanism in the respiratory system that helps to clear pathogens and foreign particles from the lungs. Cilia beat in a coordinated manner to move harmful substances up and out of the airways.

Host defenses in different regions of the body include immune cells that target pathogens, mucus that traps invaders, skin barriers that prevent entry, and acidic environments that inhibit bacterial growth. Hormones, vitamins, and minerals do not directly act as host defenses. Blood flow, heart rate, and lung capacity are physiological functions, not host defenses. Nerves, bones, and muscles play roles in bodily functions but are not primary host defenses.

Helicobacter pylori employs a combination of strategies, including urease production, protection against gastric acid, and adhesin production, to survive in the host's stomach.

The correct answer explains the specific strategy of bacterial invasion to evade the immune system, while the incorrect answers provide alternative and incorrect methods that bacteria do not utilize.

The normal flora (microbiota) has a symbiotic relationship with the human body, providing benefits such as maintaining a balanced microbiome which is crucial for overall health and disease prevention.

The complement cascade can be initiated through the classical pathway, lectin pathway, or alternative pathway, involving different recognition molecules and triggering mechanisms.

The Classical pathway involves specific steps including the formation of an active C1 complex, cleavage of C4 and C2, and subsequent cleavage of C3 into C3b. The incorrect answers provided do not accurately describe the Classical pathway and its mechanisms.

The correct description of the Lectin Pathway involves Mannose binding lectin associated with MAS (Mannose-binding lectin Associated Serine Protease) and activation of serine proteases that cleave C4 and C2, leading to the formation of the convertase.

Factor H and Factor I play a crucial role in regulating the complement cascade to prevent host cells from being attacked by the immune system.

During the complement system cascade, C3 undergoes a series of steps involving cleavage, exposure of a thioester bond, binding to surfaces, cleavage into smaller fragemnts, and eventual degradation. This process is crucial for the activation of the complement system and its role in immune responses.

C4 binding protein plays a crucial role in regulating the complement cascade by inhibiting the formation of the C3 convertase complex. This prevents excessive activation of the complement system, which could lead to harmful effects on host cells. The incorrect answers provided do not accurately reflect the function of C4 binding protein and its role in complement cascade regulation.

Pseudomonas aeruginosa inhibits the complement cascade by evading the classical pathway/mannose-binding lectin via alkaline protease (AprA) secreted by the pathogen.

Yersinia enterocolitica inhibits the complement cascade by specifically targeting the alternative pathway through YadA binding factor H, leading to a series of interactions that prevent complement activation.

Haemophilus influenzae inhibits the complement cascade by producing proteins that interfere with the different pathways and components of the cascade, preventing its activation.

Haemophilus influenzae inactivates C4b by bringing in factor I to prevent the cascade from continuing and also utilizes outer membrane proteins to prevent MAC insertion into the surface.

Haemophilus influenzae evades the host immune response by inactivating C3b, an important opsonin involved in the complement system.