Human blood CD4+ cells also include some subsets of APCs (e.g.
plasmacytoid DCs are CD4+). Apart from this, a 98% purity means some
CD4- APCs are likely to be co-cultured, too : as a superantigen can
activate up to 20% of all CD4+ T lymphocyte clones, even a minimal
presence of APCs could explain such a quite massive in vitro
activation with Th1 polarization. Despite there is some evidence SEB
could act via TLR4 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12020131),
TLR4 is highly expressed only in monocytes and B cells (and weakly
expressed in neutrophils and basophils), so it can not account for T
cell activation in absence of APCs.
Hope this helps.
Daniele Focosi
(Molecular Immunology : http://www.mi.interhealth.info)
eak at medicine.wisc.edu (Becky Kelly) wrote in message news:<15db76ed.0404021133.1bdfd572 at posting.google.com>...
> Can anyone tell me if circulating human CD4+ T cells can be directly
> (absence of APCs)activated by SEB? Human blood CD4+ cells were sorted
> by FACS to >98% puriety. Cells were stimulated for 6 days with SEB (3
> micrograms/ml)and sups analyzed by ELISA for IL-13 and IFN-gamma. Very
> high cytokines levels were seen (100 ng/ml IFN-g and 5 ng/ml IL-13).
> Any thoughts on mechanism? Does SEB bind to a TLR?
> Thanks-Becky
