Immunohistological Detection of Growth Factors and Cytokines in Tissue Mast Cells

The relative rarity of mast cells (MCs) and the rich content of heparin in the cytoplasmic granules of MCs pose technical challenges in reliably detecting growth factors (GFs) or cytokines in MCs by conventional immunohistological stain (IHS) methods. A variety of polypeptide growth factors are characterized by high-affinity to heparin. Binding of GFs to MC granules during detection can lead to highly specific yet falsely positive results that cannot be easily discovered by conventional procedure controls. Many reagents used in IHS detection or related experiments contain GFs and are potential nonphysiological sources of the detected GFs in MCs. In addition, heparin also exhibits high binding affinity to avidin and streptavidin, key components of the most widely used IHS detection and amplification system. Although biotin-avidin-free detection systems are readily available and are highly recommended for the future studies in this field, the vast majority of the studies of GFs in MCs in the literature have used biotin-avidin-based methods. In this chapter, the inherent technical pitfalls related to the aforementioned features of MCs, and suggested solutions are presented. They are intended to provide technical assistance to investigators in this field and to help interpret the results of the past studies in the literature.