Extracellular pathogens

Question 1

What must happen for infection to occur?

Answer 1

Pathogen must penetrate epithelium and establish infection.

Question 2

How do extracellular microbes spread through the body?

Answer 2

Through the lymphatics or bloodstream.

Question 3

Where do naïve lymphocytes enter lymph nodes?

Answer 3

Through high endothelial venules (HEVs).

Question 4

How do lymphocytes return to the bloodstream?

Answer 4

Via efferent lymphatics → thoracic duct.

Question 5

What chemokine receptor directs naïve T cells to lymph nodes?

Answer 5

CCR7, responding to CCL19/CCL21.

Question 6

What attracts B cells into follicles?

Answer 6

CXCL13 binding CXCR5.

Question 7

What initiates rolling of lymphocytes on HEVs?

Answer 7

L-selectin binding GlyCAM-1/CD34.

Question 8

What mediates firm adhesion of lymphocytes to HEVs?

Answer 8

LFA-1 binding ICAM-1.

Question 9

What guides T-cell exit from lymph nodes?

Answer 9

The S1P gradient sensed by S1P₁ receptor.

Question 10

How is T-cell exit prevented during activation?

Answer 10

Activated T cells upregulate CD69, which suppresses S1P₁.

Question 11

How do naïve B cells enter lymph nodes?

Answer 11

Via HEVs using CCR7 and CXCR5.

Question 12

Where do activated B and T cells first interact?

Answer 12

At the T–B border of lymph nodes.

Question 13

What forms the germinal center?

Answer 13

Activated B cells + T follicular helper (Tfh) cells.

Question 14

What cell type secretes CXCL13 in germinal centers?

Answer 14

Follicular dendritic cells (FDCs).

Question 15

What is the primary function of the spleen?

Answer 15

To filter blood-borne antigens.

Question 16

What does the PALS region of the spleen contain?

Answer 16

T-cell activation zones.

Question 17

What does the marginal zone of the spleen contain?

Answer 17

Macrophages and marginal zone B cells.

Question 18

Why are asplenic patients at higher infection risk?

Answer 18

They cannot efficiently clear encapsulated bacteria.

Question 19

What is the main function of mucosal immunity?

Answer 19

Protect mucosal surfaces without causing inflammation.

Question 20

What are Peyer’s patches?

Answer 20

Lymphoid tissues in the small intestine containing B cells and APCs.

Question 21

What is the function of M cells in Peyer’s patches?

Answer 21

Transcytose gut antigens to underlying immune cells.

Question 22

Which integrin helps activated T cells home back to gut mucosa?

Answer 22

α4β7 integrin.

Question 23

What chemokine receptor directs activated T cells to the gut lamina propria?

Answer 23

CCR9.

Question 24

What drives IgA class switching in the gut?

Answer 24

TGF-β secreted by T cells.

Question 25

What is the role of secretory IgA?

Answer 25

Neutralizes pathogens and toxins at mucosal surfaces without inflammation.