Cells and Lymphoid Organs of the Immune System

Natural killer cells

lymphocytes that can kill host cells without making their own antigen-specific receptor
innate immunity only

CD markers

specific types of molecules found on the surface of cells that help differentiate one cell type from aother

Monocyte

differentiate into macrophages

macrophages

2-13% of white blood cells
increase in size 5-10 fold
increased phagocytic ability
high level of hydrolytic enzymes
secretes variety of soluble factors
professional antigen presenting cells

activated macrophages

digest exogenous antigens
use oxygen-dependent killing by reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI)
perform oxygen-independent killing via various hydrolytic enzymes
have antimicrobial and cytotoxin peptides called defensins
secrete tumor necrosis factor-alphs
express high levels of class II MHC and peptide complexes with class I MHC

respiratory burst

the process by which ROI are produced
the membrane bound oxidase catalyzes the reduction of oxygen to superoxide anion

Opsonin

a molecule (anitbody or complement component C3b) that binds to antigen and macrophage thereby enhancing phagocytosis

opsonization

process by which particulate antigens are rendered suseptible to phagocytosis

Neutophils

infection causes and increase
1st to arrive at site of inflammation
kill microorganism
makes hypochlorous acid (bleach)

Eosinophils

phagocytic cells
bilobed nuclei
defense against parasitic organisms

Mast cells

play a crucial role in inflammatory and immediate allergic responses
leave the bone marrow undifferentiated, enter tissues and then differentiate
release potent inflammatory mediators that act on vasculature, smooth muscle, connective tissues, mucous glands, and inflammatory cells

Basophils

least numerous of leukocytes
play a crucial role in inflammatory and immediate allergic responses
release potent inflammatory mediators that act on vasculature, smooth muscle, connective tissues, mucous glands, and inflammatory cells

Dendritic cells

antigen presenting cells
capture antigen in tissues and then go to lymphoid organs to present the antigen to T lymphocytes

Langerhans cells

dendritic cells in the skin

interstital dendritic cells

dendritic cells in connective tissue of most organs

interdigitating dendritic cells

dendritic cells in lymphoid cells

circulating dendritic cells

dendritic cells in the bloodstream

follicular dendritic cells

dendritic cells in lymph nodes
not professional APC, they capture immune complex and present to B cells

Primary Lymphoid organs

sites of lymphocyte maturation
bone marrow and thymus

Thymus

arranged into an outer cortex and an inner medulla
immature lymphoid cells enter the cortes where they proliferate, mature and pass on into the medulla. From the Medulla, mature T cells enter the circulation
Where T cell receptor rearrangement occurs

T cell receptor rearrangement

the elimination of T cells that cannot recognize antigen-MHC complex and that recognize self antigens

Digeorge’s syndrome

congenital birth defect in humans that results in a lack of thymus

bone morrow

B cell development occurs here in adults
B cell development is complete and B cells are functionally mature when they exit here

liver

where B cell development occurs during embryotic development

Secondary lymphoid organs

site of lymphocyte activation
lymph nodes
mucosal associated lymphoid tissue (MALT)
Spleen

Lymph Nodes

bean shaped structure that filter antigens from lymph

follicles

where B cells enter the lymph nodes

paracortex

where T cells enter the lymph nodes

Cortex

part of the lymph node that contains mostly B cells, follicular dendritic cells and macrophages arrange in clusters called primary follicles
contains the germinal center

germinal center

contains proliferating B cells and plasma cells interspersed with macrophages and dendritic cells

spleen

Immune response against blood borne antigens
filters the blood

red pulp

part of the spleen that contains macrophages and red cells
site at which old and defective red cells are destroyed

white pulp

part of the spleen that surrounds the splenic artery forming the periarteriolar lymphoid sheath (PALS) that is populated mainly with T cells

Primary lymphoid follicles

are attached to PALS, are rich in B cells, come of them are within the germinal centerM

Marginal zone

is peripheral to PALS and contains macrophages and lymphocytes

MALT

organized lymphoid tissues that line mucous membranes lining the digestive, respiratory and urogenital systems

Cutaneous-Associated Lymphoid Tissue

langerhans cells are found in the epidermis. These cells can trap antigens and present them to T cells which are also present as intraepithelial lymphocytes