Kristen,
To me something like CD3 is the way to go if I understand your project as you described it.  Something like SATB1, which I've never used by IHC but know something about, seems like overkill or using a good (but incorrect) tool for the job.  SATB1 (special AT-rich binding protein 1) I'm sure works well in Marks hands and others.  But it is a not well characterized molecule being a loop-folding domain transcriptional regulator and while true found "mainly" in thymocytes, there are certainly indications of its presence in myeloid and erythroid precursors as well as developing mouse CNS.  And it can be upregulated and down-regulated.  And probably Marks statement that there might be anti-rat SATB1 (and SATB2) antibodies around is true, but might not be so easy to find or use.  Compare that to the absolutely, precisely characterized and described gamma/delta/epsilon/zeta/eta CD3 TCR complex.  It has been studied in minute detail all over the world, its presence or absence in cell types 
is documented and redocumented countless times.  The number I've heard is about 10,000 copies per T-cell and literally defines that cell.  If you wanted to "mark" T-cells in flow, frozen or paraffin I think 99% of labs would use CD3 at some point whether in periphery or thymus.  Well characterized and protocoled anti-rat CD3 IHC antibodies exist in multiple clones and from multiple vendors for rat IHC.  I like BD Pharmingen but just my opinion. Without ever having stained for SATB1 in rat, I believe what was said and guess yes you could do it, the question is, is that the easiest and most efficient way to get to your answer?

Ray Koelling
PhenoPath Labs
Seattle, WA

-------------- Original message -------------- 
From: "Kristen Broomall"  

> Good Morning all, I was wondering if anyone had suggestions on an antibody 
> to detect T cells (only, no B cells) in formalin fixed, paraffin embedded 
> rat thymus and spleen. I have a Pan T Cell marker that is working well in 
> the spleen, but so-so in the thymus, so I think that it is only staining the 
> mature T cells, and not immature cells (which of course, is what we also 
> need to see). I've been reading up alot on T cells and trying to figure this 
> out (CD3, CD4, CD8, TCR, lions, tigers and bears - Oh My!), but I fear our 
> deadline for getting staining done is shorter than the time I have to 
> educate myself properly! 
> 
> Any suggestions would be greatly appreciated! 
> 
> 
> Happy Holidays, 
> Kristen Broomall, HT (ASCP) 
> histotechkb@gmail.com 
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