Secondary (2Secondary (2oo) Lymphoid Tissues) Lymphoid Tissues

Adapted from Roitt’s Immunology 7-1

What happens in 2What happens in 2oo lymphoid lymphoid tissues?tissues?

1.1. Highly efficient in trapping and Highly efficient in trapping and concentrating foreign substances concentrating foreign substances carried in the blood and lymphcarried in the blood and lymph

2.2. They are the main sites of They are the main sites of production of production of _antibodies__antibodies_ and and induction of antigen-specific T cellsinduction of antigen-specific T cells

Why is that important?Why is that important?

In a naïve (non-immunized) animal, only In a naïve (non-immunized) animal, only 1 in a 1,000 to 1 in 100,000 1 in a 1,000 to 1 in 100,000 lymphocytes can recognize the typical lymphocytes can recognize the typical foreign invaderforeign invader

Lymph NodesLymph Nodes

Abbas & Lichtman’s Basic Immunology 1-14 & 1-16

-The lymph node has specific region for both T cells (Paracortex) and B cells (Follicle).

-Lymphocytes enter the node via the blood while antigens enter via the lymph vessels.

-Both cell types encounter and respond to antigens in their respective zones.

Lymph NodesLymph Nodes

Abbas & Lichtman’s Basic Immunology 1-17

Native T cells migrate into the lymph node via the bloodstream and become activated by antigens.

The activated T cells exit the nodes via both the bloodstream and the lymph system where they can migrate to peripheral sites of infection.

Lymph NodesLymph Nodes

Lymph fluidLymph fluid Lymph fluid from tissues drains Lymph fluid from tissues drains

into regional lymph nodes.into regional lymph nodes.

APCAPC APC in the lymph nodes can sample APC in the lymph nodes can sample

microbial antigens from the lymph microbial antigens from the lymph fluid.fluid.

Roitt’s Immunology 7-3

Lymphocyte RecirculationLymphocyte Recirculation

Naïve lymphocytesNaïve lymphocytes Migrate from lymph node to lymph node looking Migrate from lymph node to lymph node looking

for an APC to present the correct antigen to it.for an APC to present the correct antigen to it. Effector lymphocytesEffector lymphocytes

Migrate to the site of infection (T cell)Migrate to the site of infection (T cell) Secrete antibody from lymphoid organ (B cell)Secrete antibody from lymphoid organ (B cell)

80% of lymphocytes migrate to a different 80% of lymphocytes migrate to a different lymph node each daylymph node each day

Abbas & Lichtman’s Basic Immunology 1-17

SpleenSpleen

The The T cellsT cells are segregated to theare segregated to the periarteriolar periarteriolar lymphoid sheath (PALS)lymphoid sheath (PALS)

The The B cellsB cells are segregated to theare segregated to the secondary secondary folliclefollicle

Same role for blood-borne antigen as lymph node Same role for blood-borne antigen as lymph node does for lymph-borne antigen.does for lymph-borne antigen.

Abbas & Lichtman’s Basic Immunology 1-15

Mucosa-associated Lymphoid Tissue Mucosa-associated Lymphoid Tissue (MALT)(MALT)

Mucous - acts to trap microorganisms, allowing Mucous - acts to trap microorganisms, allowing them to be swept away by ciliated epithelial them to be swept away by ciliated epithelial cells towards external openingscells towards external openings

Loose lymphoid aggregates that line mucosal Loose lymphoid aggregates that line mucosal epitheliumepithelium

Non-encapsulated lymphoid tissues (as opposed Non-encapsulated lymphoid tissues (as opposed to spleen and lymph nodes)to spleen and lymph nodes)

Cells of the MALT tend to recirculate only to Cells of the MALT tend to recirculate only to other mucosal tissuesother mucosal tissues

Typically found in the GI system where it is Typically found in the GI system where it is termed GALT (Gut-associated Lymphoid Tissue)termed GALT (Gut-associated Lymphoid Tissue)

Tissues of the Immune SystemTissues of the Immune System

Adapted from Sherwood’s Human Physiology Table 12-1

Next TimeNext Time

Describe the innate immune system.Describe the innate immune system. Compare and contrast the innate Compare and contrast the innate

immune system with the adaptive immune system with the adaptive immune system.immune system.

Readings: Abbas & Lichtman, Readings: Abbas & Lichtman, Chapters 1 & 2Chapters 1 & 2

ObjectivesObjectives

1.1. Describe the normal functions of the Describe the normal functions of the immune system.immune system.

2.2. Describe the cells and tissues of the Describe the cells and tissues of the immune system.immune system.

3.3. Describe the maturation process of Describe the maturation process of lymphocytes.lymphocytes.