The "early' CD4+CD8+ stage of thymocte differentiation hallmarks the end of a strong positive correlation between extracellular matrix receptor expression and protein tyrosine phosphorylation.
We used irradiation-induced thymic regression/reconstitution to study phosphotyrosine (PTyr) levels and expression of extracellular matrix receptors in thymocyte subsets by flow cytometry. High PTyr levels (PTyr(hi)) characterized cells from the CD4-CD8-(DN)CD25in/hi to the "early" CD4-CD8+(DP)CD25- stage. Correlation indexes (R) between the percentages of these PTyrhi cells and cells with up-regulated expression of alpha4 integrin (alpha4hi) were strongly positive (R= 0.91, P= 0.002, for DN; R= 0.98, P= 0.0001 for DP). At the "early" DP stage, R between PTyrhi cells and cells with up-regulated expression of alpha5 integrin and L-selectin (alpha5hi and L-sel(hi)) also rendered strongly positive (R>0.95, p<0.0003). "Late" expanding DP cells exhibited intermediate PTyr levels (PTyr(in)), associated with a down-regulation of the adhesion receptors assessed. Triple-labeling suggested that in most early CD3-/lo cells, alpha4hi and alpha5hi, but not L-sel(hi) expression preceded a PTyr(hi) content. CD3in/hi-enriched CD8+ cells were also PTyr(hi), but conversely to the immature ones exhibited a tendency for a negative R between PTyr(hi) and alpha4hi (R = -0.93, P = 0.067, n= 4) or alpha5hi cells (R = -0.77, P = 0.23, n = 4). CD4+ cells were either PTyr(hi) or PTyr(in), exhibiting a tendency for a positive R (R = 0.59, P = 0.124, n= 8) between PTyr(hi) and L-sel(hi) cells only. In conclusion, our results associate an up-regulation of alpha4 and alpha5 chains expression with PTyr(hi) levels and, as elsewhere published, with increased adhesion to fibronectin up to the "early" DP stage, but not afterwards.
Dalmau
S R
SR
Division of Experimental Medicine, Basic Research Center, National Cancer Institute, Rio de Janeiro, RJ, Brazil. dalmau@openlink.com.br
Freitas
C S
CS
Savino
W
W
D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis*; D017209:Apoptosis; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology*; D002454:Cell Differentiation; D005109:Extracellular Matrix / Q000378:metabolism*; D005260:Female; D039441:Integrin alpha4; D039564:Integrin alphaV; D019041:L-Selectin / Q000096:biosynthesis*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism*; D016176:T-Lymphocyte Subsets / Q000166:cytology; D014916:Whole-Body Irradiation
D015703:Antigens, CD; D039564:Integrin alphaV; D019041:L-Selectin; D039441:Integrin alpha4; D019000:Phosphotyrosine