We do frozens exclusively for research IHC 

Protocol is 

snap freeze tissue, cut at desired thickness,air dry overnight, if in a
humid area use a dessicator with silica gel.  Fix next day in acetone
75%/absolute alcohol 25% 5 min at RT, go directly to two changes of PBS,
stain.

Have used 4C acetone on air dried sections (30 min to 4 hours, even
overnight) but sections never looked as great as they do now.  Remember
that some fixatives may work better for some antigens.

Have tried acetone/alcohol at 4C also, gave good morphology.

My murine CD4 is now out to 1:20,000 using this fixation protocol, so I
have not lost anything, but morphology is wonderful compared to acetone
alone. 

We also do a glucose oxidase/glucose/sodium azide endogenous peroxidase
block.  

I can thank Barb Wright for this improved fixation method. 
Gayle Callis
Veterinary Molecular Biology
Montana State University
Bozeman MT 59717-3610
406 994-4705
406 994-4303