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36 Part one Principles of Immune Response

sebaceous glands. The dermal vasculature includes an extensive
network of plexuses with arterioles, capillaries, and venules.
Dermal lymphatics are associated with the vascular plexuses. In
Bronchiole normal skin, a small number of lymphocytes can be found in
with mucus
perivascular areas. These lymphocytes are mostly T cells with
distinctive features, including expression of a memory phenotype
(CD45RO) and expression of a cutaneous lymphocyte–associated
antigen that binds to the vascular addressing endothelial cell
leukocyte adhesion molecule-1 (ELAM-1, or CD62E) present
on the endothelium. This latter interaction plays an important
role in homing of memory T cells to inflamed regions of skin.
The dermis also contains mast cells important for immediate
hypersensitivity reactions. Tregs are abundant in the skin. CD8
Lymphoid T cells are common in the epidermis. CD4 T cells are common
aggregate 57
in dermis infected with shingles.
Blood
vessel Commensal Organisms/Toll-Like Receptors
Humans live in symbiosis with over 1000 different species of
viruses, bacteria, protozoa, and fungi that far outnumber human
cells. Collectively termed commensal microbiota, these organisms
are essential to the development, maturation, organization, and
Lung regulation of the mucosal immune system. Many of their
58
A tissue immune interactions involve TLR triggering. TLRs activate and
prime both innate and specific immune responses. Production
of IgA, induction of regulatory T cells, and stimulation of
antiinflammatory cytokines are associated with commensal
59
microbiota. Thus the types and quantities of microorganisms
present at a mucosal surface is an important component of the
mucosal immune response. 60

on tHe HorIZon

• Understanding how stem cells self-renew is a key to exploiting them
for gene therapy.
• Exploiting innate and acquired immune cell function requires an
understanding of the multiple subpopulations of cells and the manner
in which they are induced.
• Increasing generation of new T cells and B cells later in life might
enhance immune function, and thus prolong quality of life.
• The role of adipose tissue in hematopoietic stem cell (HSC) development
in bone marrow and control of inflammation in obesity is fundamental
to controlling the epidemic of obesity.
• Exploiting interactions between the mucosal immune system and
commensal populations may improve health, prevent inflammation,
and lead to less antibiotic use.
• Cellular migration via the lymphatics to the brain is unknown; inflam-
mation and cancer spread might be reduced by controlling inflammation
B of the lymphatics.
FIG 2.11 Lymphoid regions in the human lung.
ACKNOWLEDGMENTS

We thank Dr. Gregory R. Harriman at BioAdvance for his work
on previous editions of this chapter; Dr. Edwina Popek, Pathology
enter the afferent lymphatics, and migrate to draining lymph Department, Texas Children’s Hospital, Houston, Texas, for
nodes. There they present antigen to T cells to promote primary providing histopathologic images of lymphoid tissues; Dr. Gregory
immune responses. Other types of dermal DCs, including those Stelzer and Wendy Schober for the flow cytometric display;
that are macrophage-like, expressing CD14, and those that are Eleanor Chapman, Anna Wirt, Terry Saulsberry, Yvette Wyckoff,
DC-like, expressing CD1c and CD14, have consequences for and Pamela Love for help with the manuscript; and Dr. Jerry
atopic dermatitis and psoriasis. 57 McGhee for critical review of the first edition.
The dermis lies under the epidermis. It contains abundant
fibroblasts producing collagen, a principal component of skin. Please check your eBook at https://expertconsult.inkling.com/
The dermis also contains blood vessels and various epidermal for self-assessment questions. See inside cover for registration
adnexal structures, such as hair follicles, sweat glands, and details.