Explain how the normal microbiota is involved in immunity and the various relationships the microbiota can be in. (USLO 7.1)
Discuss the difference between innate and adaptive immune responses. Be sure to include first, second, and third lines of defense. (USLOs 7.2 and 7.3)
Explain the difference between cell-mediated versus humoral responses. Be sure to include cell types and function of each response. (USLO 7.4)
Discuss the different types of vaccines. Be sure to include the advantages and disadvantages of each type. (USLO 7.5)
Attenuated
Heat Killed
Subunit
Toxoid
Conjugate
Explain the concept of herd immunity and how vaccination is involved. (USLO 7.6)
Commensalism: One organism benefits, while the other is neither harmed nor helped. Many bacteria living on our skin are commensals, as they feed on dead skin cells and oils without affecting us.
Parasitism: One organism benefits at the expense of the other, causing harm or disease. This occurs when a member of the normal microbiota becomes an opportunistic pathogen, causing disease when the host's immune system is weakened.
Innate vs. Adaptive Immune Responses
The immune system operates with a multi-layered defense strategy. The innate immune response is the body's non-specific, immediate reaction to a pathogen. It is a general defense system that is present from birth and does not get better with repeated exposure. The adaptive immune response, in contrast, is a specific, learned, and highly effective defense that develops over time. It "remembers" pathogens it has encountered before, allowing for a faster and stronger response upon subsequent exposure.
The three lines of defense are:
First Line of Defense: This includes physical and chemical barriers that prevent pathogens from entering the body. These are part of the innate immune system.
Physical barriers: Skin, mucous membranes, cilia, and tears.
Chemical barriers: Stomach acid, lysozyme in tears and saliva, and antimicrobial peptides.
Second Line of Defense: This is an innate, non-specific internal defense system that acts once a pathogen has entered the body.
Inflammatory response: Swelling, redness, pain, and heat, which bring immune cells to the site of infection.
Phagocytosis: Specialized white blood cells like neutrophils and macrophages "eat" and destroy pathogens.
Fever: Elevated body temperature can inhibit the growth of some pathogens.
Third Line of Defense: This is the adaptive immune response. It is a highly specific and targeted defense that relies on lymphocytes (B and T cells) to recognize and eliminate specific pathogens. It also creates a memory of the pathogen to prevent future infections
Sample Answer
The normal microbiota plays a crucial role in immunity by acting as a first line of defense and educating the immune system. They do this by occupying colonization niches, which prevents pathogens from establishing themselves, a concept known as competitive exclusion. They also produce antimicrobial compounds that can kill or inhibit the growth of harmful bacteria. Furthermore, the presence of the microbiota trains the immune system from a young age, helping it to distinguish between harmless foreign substances and dangerous pathogens.
The relationships between the microbiota and their host can be described in three main ways:
Mutualism: Both the host and the microbe benefit from the relationship. An example is the relationship between humans and E. coli in the gut, where the bacteria receive nutrients and a stable environment, while in return, they produce vitamin K, which is essential for blood clotting.