- TH 1 response is primarily directed toward macrophages and T cells and
the support of the inflammatory response. - TH 2 response is primarily directed toward B cells and therefore antibody
responses.
Treg cells are CD4+, express CD25 and produce IL-10 and TGF-beta,
lymphokines that are both strong immunosuppressants inhibiting TH1 and
TH2 cells.
NK cells are not T cells, but kill cellular targets such as tumor cells in a
nonspecific manner.
Organs
Lymphoid organsmay be either primary(bone marrowandthymus) or
secondary(lymph nodesanddispersed lymphatic nodules, spleen,
andtonsils). The B lymphocytes are educated in the bone marrow [differ-
entiation of antigen-binding receptors (antibodies)] and are seeded to spe-
cific B cell regions of the secondary lymphoid organs, while T lymphocytes
are educated in the thymus [differentiation of T cell receptors (TcR)] and
are seeded to T cell-dependent regionsof the secondary lymphoid organs.
Thethymusis recognized by lobulation, separate cortex and medulla
in each lobule,theabsence of germinal centers,and the presence of
Hassall’s corpuscles.Thelymph nodes,whichfilter lymph and blood,are
characterized by a central medullaconsisting of cords with many plasma
cells and a cortex containing primary and secondary follicles.Thespleen,
whichfilters blood,is characterized by red and white pulp.Thetonsils
are characterized by crypts with an epithelial lining on one side. That lin-
ing is stratified squamous epithelium in palatine tonsils and pseudostrati-
fied epithelium on pharyngeal tonsils.
RESPIRATORY SYSTEMThe respiratory epithelium consists of conducting pathways(nasal cavi-
ties, naso- and oropharynx, larynx, trachea, bronchi, and bronchioles) and
respiratory portions(respiratory bronchioles and alveoli). The nasal
epithelium includes a region of specialized olfactory receptors. Ciliated
cells appear in all portions of the respiratory system except the respiratory
epithelium and move mucus and particulates toward the oropharynx
(mucociliary escalator).Gas exchange in the lungs takes place across a
minimal barrierconsisting of the capillary endothelium, a joint basal
lamina, and an exceedingly thin alveolar epitheliumconsistingprimarily
High-Yield Facts 27