EXPRESSION OF KERATOHYALIN TRICHOHYALIN HYBRID GRANULES IN MOLLUSCUM CONTAGIOSUM

Background. Recently, in the filiform papillae epithelium of mouse dor sal tongue, we showed the presence of hybrid granules in which filaggr in and trichohyalin were both present, but physically segregated. Furt her, trichohyalin was also detected in scattered granular cells of a n umber of hyperplastic skin diseases. Methods. The epidermis infected w ith molluscum contagiosum virus (MCV) was studied by conventional elec tron microscopy in conjunction with light and electron-microscopic imm unohistochemistry, using both antifilaggrin and antitrichohyalin antib odies as probes. Results. We found that the granular cells of MCV-infe cted epidermis contained both filaggrin and trichohyalin. Subsequent e lectron-microscopic examination showed that the granular cells contain ed morphologically heterogeneous granules that appeared to be composed of discrete areas of distinct electron densities. Double-labeling, us ing antibodies to filaggrin and trichohyalin, clearly indicated that f ilaggrin and trichohyalin were both present in the hybrid granules and that the electron-dense regions contained trichohyalin while the more electron-lucent regions contained filaggrin. Conclusions. The express ion of trichohyalin was a common feature observed in the epidermis fro m a heterogenous group of hyperplastic conditions, including MCV infec tion. This finding has led us to speculate that trichohyalin may be sp ecifically or preferentially involved in interacting with the hyperpro liferation-related keratin pair (K6/K16), whereas the function of fila ggrin is more closely linked to the skin-type keratin pair (K1/K10) th at are normal keratins found in the differentiated epidermis.