Positivity is confined to collagen type I fibres ( coating them) most obviuosly seen in the submucosa

Note that what appear to be medullary cells have a very strong cytoplasmic positivity ? specific? The positivity seen in the collagen of the developing skeletal muscles fibres (to the left of adrenal ) is as expected.

I used anti IgM-biotinylated  secondary ( anti IgG-biotin gave identical intensity of +ty but section quality was poor). I noted CS-+ve extracellular “plaques” in the white matter ( so are not Amyloid plaques)

This was originally 5 cryosections stored in antifreeze. I tipped off the antifreeze and added excess Formalin to fix overnight with gentle agitation ( at RT). I then processed sections to Pwax and cut conventionally. Immunostaining was excellent.

One may do this conversion procedure succesfully with unfixed/fixed frozen tissues

This was originally 5 cryosections  stored in antifreeze. I tipped off the antifreeze and added excess Formalin to fix overnight with gentle agitation ( at RT). I then processed sections to Pwax and cut conventionally. Immunostaining was excellent

One may substitute anti IgM with anti IgG, imho.

The non-neuronal interstitial tissue +ty in both appears to be equal. However, the neuropil ( CNS interstitial tissue) is less intensely +ve when using anti IgM-biotinylated secondary.

Comments welcome

ExCuticle: one can see plenty of goblet cells and even some secretions.