RT Book, Section
A1 Jacobson, Amanda
A1 Nadeau, Kari
A2 Stevenson, David K.
A2 Cohen, Ronald S.
A2 Sunshine, Philip
SR Print(0)
ID 1109799573
T1 T-Cell Dysfunction
T2 Neonatology: Clinical Practice and Procedures
YR 2015
FD 2015
PB McGraw-Hill Education
PP New York, NY
SN 9780071763769
LK accesspediatrics.mhmedical.com/content.aspx?aid=1109799573
RD 2024/04/23
AB T  cells  are  major  effector  cells  of  the  adaptive  immune  response  from  influencing  antibody  production  to  maintaining  tolerance.  The  defining  marker  of  the  T  cell  is  the  T-cell  receptor  (TCR),  and  2  distinct  T-cell  subsets  have  been  characterized  based  on  the  structure  of  the  TCR:  TCRα/β  and  TCRγδ.  The  specificity  of  the  TCRα/β  T-cell  repertoire  is  established  during  fetal  development  of  the  thymus,  which  develops  at  week  6  of  gestation.  Immature  thymic  cells  develop  from  fetal  liver  cells  and,  after  birth,  from  hematopoetic  stem  cells  (HSCS)  in  the  bone  marrow.  T  cells  develop  from  common  lymphoid  progenitor  cells  derived  from  HSCs  within  the  thymus  and  undergo  stages  of  differentiation,  expressing  1  or  both  of  the  cytodifferentiation  (CD)  antigens  CD4  and  CD8.  T  cells  expressing  the  α/β  TCR  are  divided  into  various  subsets  based  on  surface  CD  antigens  and  function.  CD4+  T  cells,  or  helper  T  cells  (TH),  make  up  approximately  70%  of  T  cells  in  the  peripheral  blood.  TH  cells  recognize  foreign  antigens  processed  and  presented  in  major  histocompatibility  complex  (MHC)  class  II  molecules  and  can  be  divided  into  additional  subsets.  TH1  CD4+  T  cells  produce  interferon  gamma  (IFN-γ)  and  IL-2,  favor  antibody  class  switching  to  immunoglobulin  (Ig)  G2,  and  mediate  protection  against  intracellular  pathogens.  TH2  CD4+  T  cells  produce  IL-4,  IL-13,  and  IL-5,  favor  class  switching  to  IgG1  and  IgE,  and  participate  in  atopic  diseases  and  immunity  against  parasites.  More  recently,  additional  subsets  of  CD4+  T  cells  have  been  described  that  have  effector  functions  against  extracellular  microbes:  TH9  cells  produce  the  anti-inflammatory  cytokine  IL-10  and  are  involved  in  the  host  defense  against  nematodes,  whereas  TH17  cells  secrete  IL-17,  IL-21,  and  IL-22  and  promote  protective  immunity  against  extracellular  bacteria  and  fungi  at  mucosal  surfaces.  CD8+  cytotoxic  T  lymphocytes  (CTLs)  recognize  endogenous  proteins  bound  to  MHC  class  I  molecules,  such  as  viral  and  tumor  antigens,  and  mediate  cytotoxicity  by  lysing  altered  or  nonself  cells.  A  third  class  of  T  cells  (typically  CD4+)  with  immune  suppressive  function  are  denoted  as  regulatory  T  cells  (Treg)  and  can  be  identified  (albeit  with  some  exception)  by  the  expression  of  the  transcription  facto  FOXP3  (forkhead  box  P3).  Treg  cells  are  produced  directly  from  the  thymus  (natural  Treg)  or  induced  within  the  periphery  (induced  Treg)  and  play  major  roles  in  mediating  chronic  inflammation,  allergic  disease,  and  autoimmunity.1