Intro to Immunology

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Questions and Answers

What is the primary role of antimicrobial peptides, also known as defensins, in the immune system?

To produce antibodies against viral infections

To assist in the phagocytosis of pathogens

To enhance the adaptive immune response

To disrupt the cell membranes of bacteria and fungi (correct)

Which white blood cells are crucial for the immediate response in innate immunity?

Macrophages (correct)

T cells

B cells

Natural killer cells

Opsonisation assists in which process crucial for innate immunity?

Phagocytosis of pathogens (correct)

Inflammation response

Antibody production

Activation of T cells

Which aspect distinguishes the adaptive immune response from innate immunity?

Ability to remember specific pathogens Signup and view all the answers

What function do leukocytes serve in the immune system?

To defend against infectious disease Signup and view all the answers

What is the primary function of granulocytes?

Engulf and destroy pathogens Signup and view all the answers

Which white blood cell type is most abundant in peripheral blood?

Neutrophils Signup and view all the answers

Which cell type is specifically involved in allergic responses?

Mast cells Signup and view all the answers

What activates Natural Killer (NK) cells in the presence of unhealthy cells?

Loss of MHC Class I molecules Signup and view all the answers

What is the role of eosinophils related to parasites?

Their granules contain enzymes that can damage host tissues. Signup and view all the answers

Which statement is true regarding monocytes?

They comprise about 10% of white blood cells in peripheral blood. Signup and view all the answers

What is antibody-dependent cell cytotoxicity (ADCC)?

A mechanism where CD16 on NK cells binds to antibodies to kill target cells. Signup and view all the answers

Which type of innate immune cell can directly kill virally infected or malignant cells?

Natural Killer cells Signup and view all the answers

In what circumstances are basophils activated?

During allergic reactions Signup and view all the answers

Which cell type is responsible for the activation of adaptive immunity?

Dendritic cells Signup and view all the answers

Study Notes

Antimicrobial Peptides

Defensins are secreted by epithelial cells and phagocytes
Defensins disrupt the cell membranes of bacteria, fungi and some viral envelopes

Immune System

The immune system consists of tissues, organs, cells, molecules and genes
The immune system is responsible for protection from infectious disease

Innate and Adaptive Immunity

Innate defenses provide an immediate immune response
Innate defenses are in place before an infection occurs
Innate defenses recognize common structures on groups of pathogens
Innate defenses recognize structures such as lipopolysaccharide (LPS) on gram-negative bacteria
Adaptive responses are stimulated by exposure to specific pathogens
Adaptive responses react to diverse structures specific to a particular pathogen
Adaptive defenses recognize antigens

Cells of the Immune System

Leukocytes include neutrophils, macrophages, T cells, B cells etc.
Each leukocyte has a specialised function and role in the immune system

Macrophages

Macrophages patrol the tissues
Macrophages subsets in different tissues are given their given names, for instance Kupffer cells in the liver

Phagocytosis

Phagocytosis is the internalization of particulate matter by engulfment
Phagocytosis results in a vesicle (phagosome) that contains ingested material
Phagocytosis is an important process for eliminating pathogens, foreign material, cell debris, apoptotic cells and damaged tissue

Steps of Phagocytosis

Phagocytosis involves:
- Adherence of the phagocytes to the target
- Ingestion of the target by the phagocyte
- Formation of the phagosome
- Fusion with lysosomes
- Killing and digestion
Inductable Nitric Oxide (iNOS) synthase and Reactive Oxygen Species (ROS) are involved in the killing and digestion stages

Opsonisation

Some microbes are difficult to phagocytose
Opsonisation is the coating of a microbe with proteins, such as antibodies or complement, that facilitate phagocytosis
Acute phase proteins produced by the liver, such as C reactive protein (CRP), bind to phosphocholine on bacteria and act as an opsonin
Opsonins are recognised by receptors on phagocytes

Phagocytes

Phagocytes include:
- Macrophages
- Granulocytes: neutrophils, eosinophils and basophils
- Immature dendritic cells
Phagocytes primarily engulf and destroy pathogens
Immature dendritic cells activate adaptive immunity

Neutrophils

Neutrophils are granulocytes
Neutrophils are the most abundant white blood cells in peripheral blood
Neutrophils have multi-lobed nuclei
Neutrophils are not generally found in tissues unless recruited there
Neutrophils typically have a short lifespan after activation

Monocytes

Monocytes are agranulocytes
Monocytes represent ~10% of white blood cells in the peripheral blood

Eosinophils

Eosinophils are granulocytes
Eosinophils are found in low numbers in the blood
Eosinophil granules contain enzymes that attack parasite cell walls, but damage host tissues

Basophils

Basophils are granulocytes
Basophils are found in low numbers in the blood
Basophil granules contain potent inflammatory mediators that aid in the defense against parasites

Mast Cells

Mast cells are granulocytes
Mast cells are not found in the blood, but in the tissues
Mast cells are similar to basophils
Mast cell granules contain potent inflammatory mediators that aid in the defense against parasites
Mast cells are involved in allergic responses

Natural Killer (NK) cells

NK cells are lymphocytes part of the innate immune system
NK cells can kill host cells, for instance virally infected cells or transformed (malignant) cells
NK cells produce chemical mediators (cytokines)

NK Cell Activation

NK cells can be activated:
- By engaging activating receptors
  - CD16 binds to antibodies and activates NK cells to kill the antibody-coated cell. This process is called antibody-dependent cell cytotoxicity (ADCC).
  - NKG2D binds to NKG2D ligands upregulated in cellular and metabolic stress, such as infection and cancer, and this leads to the death of the cell
- By the loss of molecules (MHC Class I) from unhealthy cells
  - MHC Class I is present on all nucleated cells and engages inhibitory receptors (Killer Immunoglobulin-like receptors, KIR) on NK cells
  - MHC Class I can be downregulated in viral infections and cancer

Skin Barrier Function

Keratinocytes in the stratum spinosum produce β-defensins and cathelicidins (cationic peptides)
Keratinocytes in the stratum spinosum store β-defensins and cathelicidins in lamellar bodies and secrete them into the intercellular space
Β-defensins and cathelicidins act as antimicrobial agents

Barrier Function Throughout the Body

Physical and chemical barriers are widely distributed throughout the body to prevent infections
Chemical barriers include:
- Lysozyme
- Stomach acid
- Digestive enzymes
These chemical substances are microbicidal and inhibit microbial growth

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Description

Test your knowledge on the immune system, including antimicrobial peptides, innate and adaptive immunity, and leukocytes. This quiz covers key concepts and functions related to how our body defends against infection. Challenge yourself and see how well you understand these fundamental aspects of immunology.