Innate Immunity

Question 1

Which system is able to respond to a broader array of foreign motifs, innate or adaptive immunity? Why?

Answer 1

Adaptive immunity. The recombination of antigen receptor genes allows adaptive immunity to recognize 10^7 antigens. Recognition receptors used in innate immunity lack recombination ability

Question 2

Which system is better at discriminating self from nonself, innate or adaptive immunity?

Answer 2

Innate immunity. Adaptive immunity is responsible for autoimmunity, whereas there is no known autoimmunity associated with the innate immune system

Question 3

How does the innate immune system distinguish between foreign and self?

Answer 3

Innate immunity occurs in response to motifs that are characteristic of microbes but not of mammalian cells (eg, gram-negative lipopolysaccharide [LPS], gram-positive teichoic acid, and viral double stranded RNA)

Question 4

Why have microbes not adapted to avoid motifs recognized by innate immunity?

Answer 4

Innate immunity targets motifs that are indispensible to the microbe

Question 5

Why have microbes not adapted to avoid the motifs recognized by innate immunity?

Answer 5

Innate immunity targets motifs that are indispensable to the microbe

Question 6

Name the three different epithelial layers of the human body that are considered important aspects of innate immunity:

Answer 6

Skin, gastrointestinal (GI) mucosa, and respiratory epithelium. Realize that the alimentary and respiratory tracts are contiguous with the external environment

Question 7

Name the three principal effector cells of the innate immune system apart from epithelial cells:

Answer 7

1. Monocytes/macrophages
2. Neutrophils
3. Natural killer (NK) cells

Question 8

What endothelial surface structure allows rolling of leukocytes along the endothelial wall adjacent to infection?

Answer 8

E-selectins weakly bind to carbohydrate ligands on leukocytes, resulting in alternating attachment/detachment (ie, rolling along the endothelial surface).

Question 9

What endothelial surface structure allows for extravasation of leukocytes into the interstitial area of infection?

Answer 9

Vascular cell adhesion molecule (VCAM) and intercellular adhesion molecule (ICAM) bind strongly to integrins on leukocytes allowing for extracasation

Question 10

Mannose receptors and scavenger receptors are mechanisms to identify and ingest microbes utilized by what type of phagocyte?

Answer 10

Macrophages

Question 11

How do NK cells identify infected cells?

Answer 11

NK cells identify virus-infected cells by failing to identify host major histocompatibility comlex I (MHC-I). MHC-I molecules are normally present on the surface of host cells and inhibit NK celll killing, but are down-regulated when infected by viruses and other intracellular pathogens

Question 12

How do NK cells kill infected cells?

Answer 12

NK cells (and cytotoxic T cells) use perforins (create pores in the cell membrane) and granzymes (induce apoptosis)

Question 13

Deficiencies of NK cells predispose to what types of infections?

Answer 13

Intracellular infections, including intracellular microbes and viruses

Question 14

Of the three effector cells of innate immunity (macrophages, neutrophils, NK cells), which is least likely to injure host tissue?

Answer 14

NK cells, which only attack those cells lacking a host MHC-I. On the other hand, macrophages and neutrophils can injure host tissue via nonspecific reactive oxygen intermediates

Question 15

Which CD marker is useful for distinguishing NK cells from other immune cells? What is the function of this marker?

Answer 15

CD16 binds the Fc region of immunoglobulin G (IgG).

Question 16

Which of the complement pathways is considered part of the adaptive immune system?

Answer 16

The classical pathway. The alternative pathway is triggered by direct recognition of exterior features of the microbe. The lectin pathway is triggered by mannose binding lectin, which attaches to microbial surfaces containing the mannose sugar. In contrast, the classical pathway relies on IgM, IgG1 or IgG3 to recognize and attach to the microbe and thus is dependent on adaptive immunity

Question 17

What are the two main functions of innate immunity?

Answer 17

First line of defense against microbes (eg, skin and mucosa) and stimulates the adaptive immune response (eg, phagocytes act as antigen presenting cells [APCs] to induce the differentiation of T cells and secrete IL-12 to induce Th1 differentiation)