Blood Cells - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 136

Table 3.33. Helper T-cell differentiation and remodeling (Source: [ 251 ]; T H : helper T lympho-
cyte). In addition to natural, thymic-derived, CD4 regulatory T cells, naive T cells

in the periphery can become inducible, regulatory, immunosuppressive T lymphocytes (iT Reg ).
CD4

+ ,CD25 +

follicular helper T cells (T FH ) help B lymphocytes to produce antibody responses to T-
cell-dependent antigens, hence aiding in the development of germinal centers within secondary
lymphoid tissues to prom ote immunoglobulin class switch recombinatio n and affinity maturation.

+

Cell source Cell products

+

CD4 naive T cell T H1 / 2 / 17 / 22 ,T FH ,iT Reg

T H1 T FH

T H2 T H1 / 9 ,T FH

T H17 T H1 ,T FH

T FH T H1 / 2 / 17

iT Reg T H1 / 17 ,T FH

3.10.4.6 Helper T Lymphocytes

CD4 helper T cells coordinate adaptive immune defense against specific

pathogens. They secrete given sets of cytokines that signal to other subsets of
immunocytes, thereby helping B lymphocytes, CD8

+

cytotoxic T cells, as well
as other innate immunity cell types to combat given types of pathogens. T H cells
constitute many groups that do not correspond to terminally differentiated cells,
or different cell lineages, but different functional groups, as they can remodel
(Table 3.33 )[ 251 ].
Type-1 (T H1 ) and -2 (T H2 ) helper T-cell subpopulations as well as interleukin-
17-secreting helper T-cell (T H17 ) subset are the most well known. In fact, antigen-
inexperienced CD4

+

T cells specialize not only into various clones of helper T cells,
but also inducible regulatory T cells in response to infectious agents, commensal
microorganisms, and self-antigens (Table 3.34 ).
T H1

+

to protect against intracellular pathogens.
T H2 cells synthesize interleukins IL4, IL13, and IL25 to clear extracellular
pathogens. T H17 cells manufacture IL17 (or IL17a), IL17Fs, IL21, and IL22 to
target extracellular pathogens not effectively handled by other T H cells. 120

cells produce interferon- γ

T H1 Cell

T H1 -specific transcription factor is TBx21 factor. T H1 polarization is primarily due
to interleukin-12 and interferon- γ .

120 Interleukin-17 family includes 6 known members (IL17a-IL17f). Both IL17a and IL17f induce
the production of pro-inflammatory cytokines, chemokines, and metallopeptidases from various
cell types. T H cells express only IL17a, IL17f, and IL17a-IL17f heterodimer [ 226 ]. Interleukin-21
is produced by T H17 cells and ICOS

+ , CXCR5 + , CCR7 + follicular helper T cells in B-cell areas

of secondary lymphoid tissue. Interleukin-22 is synthesized by terminally differentiated T H17 cells.