I apologize for the length of this....however y'alll have the delete
button on your machines!

The question about Langerhan's cells raises some interesting problems
regarding the use of monoclonal antibodies and other markers to detect
certain antigens.
I think that first we need to be cautious in  lumping dendritic cells in
the same category as not all markers (monoclonal or otherwise) will
detect all dendritic cells even though they may have a similar lineage.
There are a large number of techniques to detect Langerhan's cells. My
wife and I have used and abused most of them over the years on sections
and sheets of mouse skin (abdomen, tail) and oral mucosae (palate,
gingiva, buccal mucosa). The gold standard for comparison of
effectiveness of detection has been frozen sections or EDTA separated,
unfixed sheets of epithelium and on unfixed cell cultures. For
histochemical techniques ATPase (afeter fixation) proved the most
effective with Non Specific Esterase a second choice.
It is well known that the surface antigens on Langerhan's cells change
with their functional condition and this can easily be seen with ATPase.
We often want to evaluate  the level  of marker, count the number of
Langerhan's cells per unit area and the overall morphology as an
indication of their functional condition. Changes in these markers can
be seen in tissue culture of these cells, in various pathologic
conditions and during the aging process. It may also be related to the
amount of time the individual cell has been within the epithelium and
the level of encounter with antigens.
It is difficult to accurately evaluate Langerhan's cells in  sections,
whether frozen or paraffin, as only a small portion of these large
dendritic cells can be seen in any one section.
As many antigens are associated with surface proteins and glycoproteins
and glycolipids, I think the question also needs to be asked as to how
the image on paraffin sections compares to the "native" state of these
cells. There are certainly differences in retention of lipids and
glycoproteins during fixation and processing. One only has to use tissue
processed using xylene as the intermediary agent compared to using
chloroform to see some major differences in binding of some antibodies
and of lectins.
If studying Langerhan's cells, then,  to me ATPase on EDTA separated
sheets still appears to be the most reliable. This is effective because
Langerhan's cells are located generally at one level in the epithelium
and because of the number of other dendritic cells in the dermis and
lamina popria that stain with the same markers. The numbers and
morphology are important because Langerhan's cells in certain pathologic
conditions and in the aging process decrease in number, have longer
dendritic processes and vary considerably in their level of some surface
antigens. The numbers can also sometimes be indicative of the prognosis
in certain pathoses.
If your aim is to detect different Langerhan's cells, for example in
chimera studies, then the use of  the appropriate Ia antigens would seem
to be indicated to detremine origin. Langerhan's cells are the only
cells in the epithelium that, under normal conditions, express this
antigen to any extent. In certain pathologic conditions, however, the
keratinocytes also show this antigen.

As well as the book already recommended, a good book for background is
Epidermal Langerhan's Cells. by G. Schuler. Published by CRC Press. Boca
Raton. 1991.

For aging in skin and oral mucosa.
The Effect of Aging in Oral Mucosa and Skin. by Christopher A. Squier
and Murray W. Hill. CRC Press. Boca Raton. 1994.

Barry