Immunobiology: Hematopoiesis, Leukocytes, Cytokines, and Lymphoid Tissues

hematopoiesis

The generation of all red and white blood cells.

When are hematopoietic stem cells first detected

3-4 weeks after conception.

hematopoiesis in adults occurs in the

axial skeleton

three main granulocytes

Neutrophils, basophils, eosinophils.

function of neutrophils

Phagocytosis and degranulation

lifespan of neutrophils

1-2 days

how quickly do neutrophils arrive at the infection site

30 minutes after acute injury or infection onset.

function of basophils

Primarily degranulation to sustain inflammatory response and sometimes phagocytosis.

eosinophils target

Large parasites, using granules with highly basic proteins and enzymes.

function of monocytes

Patrol blood, perform phagocytosis, and differentiate into macrophages or dendritic cells.

function of macrophages

Phagocytosis, secretion of cytokines, and long-lived tissue defense.

what is unique about dendritic cells

Only cell type capable of activating naïve T cells.

function of mast cells

Defense against parasites and mediation of allergies through degranulation.

cells part of lymphoid lineage

T cells, B cells, NK cells, dendritic cells.

what triggers lymphocyte priming

Binding of specific antigens leading to proliferation into lymphoblasts.

two main outcomes of lymphoblast differentiation

Short-lived effector cells and long-lived memory cells.

Cell surface proteins (sometimes co-receptors) used to identify immune cells.

CD markers

role of CD4+ T cells

Helper T cells that secrete cytokines.

role of CD8+ T cells

Cytotoxic T lymphocytes that induce cytolysis and secrete cytokines.

role of plasma cells

Secrete antibodies that bind antigens, marking them for destruction.

role of natural killer cells

Cytolytic killing of virus-infected and tumor cells.

lymphoid follicles

Cylindrical clusters of lymphocytes.

lymphoid patches

Groups of follicles.

primary lymphoid tissues

Bone marrow and thymus.

secondary lymphoid tissues

MALT, SALT, lymph nodes, spleen.

function of the spleen

Traps blood-borne antigens and recycles red blood cells.

location of the thymus

Above the heart.

positive selection of thymocytes

Ensures survival of thymocytes that bind self-MHC weakly.

negative selection of thymocytes

Elimination of thymocytes that strongly bind self-peptide-MHC.

percentage of thymocytes that survive selection

Only about 1%.

what happens to the thymus after puberty

It undergoes thymic involution (regression).

three modes of leukocyte movement

Extravasation, recirculation, homing.

leukocyte extravasation

Process by which leukocytes exit blood vessels into infected tissue.

cytokines

Soluble proteins secreted by cells to regulate immune responses, hematopoiesis, wound healing.

cytokine pleiotropy

A cytokine has multiple diverse effects on different cell types.

cytokine redundancy

Different cytokines can produce the same effect.

cytokine synergy

Cytokines working together to enhance effects.

cytokine antagonism

Cytokines blocking or masking the effects of others.

cytokine storm

Excessive uncontrolled release of cytokines, potentially fatal.

cells that mainly produce cytokines

T helper cells (Th) and macrophages.

function of IL-1

Promotes inflammation.

function of IL-6

Promotes hematopoiesis.

function of IL-10

Anti-inflammatory, immunosuppressant.

function of interferons

Antiviral and antiproliferative effects.

function of TNF

Mediates inflammation, apoptosis; linked to rheumatoid arthritis.

function of TGF-β

Immunosuppressive, important in cancer biology.

function of chemokines

Attract other immune cells (chemotaxis).

most abundant leukocytes during inflammation.

Neutrophils

How long do macrophages usually last

2-4 months

Steps of Leukocyte Extravasation

tethering, rolling, activation, arrest, crawling, transmigration

what is lymphocyte recirculation

process that allows leukocytes to move between blood and tissue

what is Lymphocyte Homing

circulating lymphocytes are selectively directed to specific tissues