Proximity Ligation Assay as a Tool for Antibody Validation in Human Tissues

Immunohistochemistry (IHC) is the accepted standard for spatial analysis of protein expression in tissues. IHC is widely used for cancer diagnostics and in basic research. The development of new antibodies to proteins with unknown expression patterns has created a demand for thorough validation. We have applied resources from the Human Protein Atlas project and the Antibody Portal at National Cancer Institute to generate protein expression data for 12 proteins across 39 cancer cell lines and 37 normal human tissue types. The outcome of IHC on consecutive sections from both cell and tissue microarrays using two independent antibodies for each protein was compared with in situ proximity ligation (isPLA), where binding by both antibodies is required to generate detection signals. Semi-quantitative scores from IHC and isPLA were compared with expression of the corresponding 12 transcripts across all cell lines and tissue types. Our results show a more consistent correlation between mRNA levels and isPLA as compared to IHC. The main benefits of isPLA include increased detection specificity and decreased unspecific staining compared to IHC. We conclude that implementing isPLA as a complement to IHC for analysis of protein expression and in antibody validation pipelines can lead to more accurate localization of proteins in tissue.

The expression and prognostic relevance of indoleamine 2,3-dioxygenase in tongue squamous cell carcinoma

Conclusion IDO might be useful for predicting progression of primary tumor stage T2 and T3 in tongue squamous cell carcinoma (TSCC), but does not seem like a specific biomarker for diagnosing TSCC and predicting patient survival. Objectives Indoleamine 2,3-dioxygenase (IDO) is expressed in many cells and it catabolises the essential amino acid tryptophan to kynurenine. IDO acts as an immune modulator through suppression of T-cell immunity and other pathways. In cancer cells, IDO has been proposed to promote tumor progression by enabling malignant cells to escape from the immune system. The aim of this study was to evaluate the association and prognostic relevance of IDO expression in TSCC. Method One hundred and eight retrospective tongue and lymph node specimens were stained immunohistochemically with monoclonal antibody anti-indoleamine 2,3-dioxygenase. The relative abundance of IDO positive epithelial cells, IDO staining intensity, and inflammation were assessed semi-quantitatively with light microscopy. Results IDO was expressed stronger in tongue hyperplasia than in TSCC. However, IDO expression associated with poor survival in the sub-groups with primary tumor stage T2-T4 and in the sub-group with strong inflammation in tumors' invasive front.

Enhanced heat shock protein 25 immunoreactivity in cranial nerve motoneurons and their related fiber tracts in rats prenatally-exposed to X-irradiation

Alterations in histoarchitecture of the brainstem were examined immunohistochemically in 4-week-old rats with a single whole body X-irradiation at a dose of 0.5, 1.0, or 1.5 Gy on embryonic day (ED) 15 using anti-heat shock protein 25 (HSP25). HSP25 immunostaining was seen in the neuronal perikarya of cranial nerve motoneurons, that is, the motor and mesencephalic nuclei of the trigeminal nerve, facial nucleus, abducens nucleus and accessory facial nucleus in the pons, and the ambiguous nucleus, dorsal nucleus of vagus nerve and hypoglossus nucleus in the medulla oblongata of intact controls. In 0.5 to 1.5 Gy-irradiated rats, HSP25 immunostaining in those neurons was more intense than in controls, while the most intense immunostaining was marked in 1.5 Gy-irradiated rats. HSP25 immunostaining was also apparent in the spinal tract of the trigeminal nerve and facial nerve tracts in 0.5 to 1.5 Gy-irradiated rats, but was faint in controls. Interestingly, HSP25 immunostaining was aberrantly enhanced in dendritic arbors in the magnocellular region of medial vestibular nucleus of 0.5-1.5 Gy-irradiated rats. Those arbors were identified as excitatory secondary vestibulo-ocular neurons by double immunofluorescence for HSP25 and SMI-32. The results suggest an increase of HSP25 expression in cranial nerve motoneurons and their related fiber tracts from prenatal exposure to ionizing irradiation. This may be an adaptive response to chronic hypoxia due to malformed brain arteries caused by prenatal ionizing irradiation.