Antigenicity testing by immunohistochemistry after tissue oxidation

AIMS

Archived tissue blocks preserve the antigenicity of samples for a long time under normal storage conditions, whereas tissue sections may show a diminished immunoreactivity over time. Little is known about the processes responsible for antigenicity loss and how tissue sections should be conserved for extended storage. Oxidation and drying are presumed mechanisms of antigenicity loss. To prove this, degradation of immunoreactivity was provoked by chemical oxidation, photo-oxidation and artificial drying.

METHODS

First, paraffin sections of an oestrogen receptor (ER) positive breast carcinoma were subjected for variable time periods to H2O2, ultraviolet A (UVA) irradiation and dry heat (56 degrees C) prior to ER immunohistochemistry. Second, using heat and UVA irradiation several other antigens (ER, PR, HER-2neu, p53, p63, p16, PSA, CK5/6, CK7, CK20, SMA, Fli-1, c-kit, CD20 and EGFR) were tested, using internal control tissue microarray sections.

RESULTS

While H2O2 had no effect on the ER-staining intensity, extended drying showed a detectable decrease in staining after 10 days, and UVA irradiation induced a decrease after 3 days. Entire antigenicity loss was not observed. Except for HER-2neu, PSA and Fli-1, all antigens showed some diminution in antigenicity, but no entire antigenicity loss, after heating and UVA irradiation.

CONCLUSIONS

This study confirms that photo-oxidation and drying have an influence on immunohistochemistry outcome, and protocols for testing the stability of specific antigens are provided.

Frequent p16/MTS1 inactivation in early stages of urothelial carcinoma of the bladder is not associated with tumor recurrence

OBJECTIVE

p16, located at chromosome 9p21, is a negative regulator of G1 cell checkpoint and functions as tumor suppressor gene. Only few data are available on the frequency and clinical relevance of p16 alterations in Ta, T1 transitional cell carcinoma (TCC) of the bladder. We investigated 40 patients with Ta, T1 TCC of the bladder for p16 alterations (mutations, homozygote deletions, allelic loss) or reduced p16 immunoreaction.

PATIENTS AND METHODS

DNA was prepared from microdissected tumor tissue from 40 patients with pTa, pT1 TCC of the bladder (pTa: 18 patients; pT1: 22 patients; grade 1: 7 patients; grade 2: 28 patients; grade 3: 5 patients). Mutation screening was performed using polymerase chain reaction (PCR), single-strand conformation polymorphism (SSCP) and direct sequencing at exon 1 and exon 2. Detection of homozygote deletions was performed using multiplex PCR. Immunohistochemistry (IHC) was performed using an anti-human monoclonal antibody (p16, Pharmingen). Allelic loss was detected by PCR using three different microsatellite markers (D9S161, D9S171, D9S319).

RESULTS

SSCP and direct sequencing revealed 3 cases of base substitution which turned out to be natural polymorphisms. Homozygote deletions were not detected in any case. p16 IHC revealed reduced p16 expression (<5% positive nuclei) in 10 patients; 30 patients had a positive reaction (> or =5% positive nuclei) and 10 patients a strong positive reaction (> or =50% positive nuclei). Thirteen of 37 informative cases revealed loss of heterozygosity (LOH) with at least one marker. After a median follow-up of 23 months, 15 patients suffered from disease recurrence. Statistical analysis using Kaplan-Meier analysis and the log-rank test did not reveal significant association of recurrence-free interval and detection of LOH (p = 0.34) or p16 IHC (p = 0.9).

CONCLUSIONS

We present a comprehensive evaluation of chromosome 9p21 alterations including p16 analysis and clinical follow-up data. Although p16 mutations and homozygote deletions are rarely detectable in Ta, T1 TCC, the reduction of p16 expression and the frequent hemizygote deletions at 9p21 suggest an early involvement of chromosome 9p and p16 in superficial TCC.