Generation of Organotypic Raft Cultures from Primary Human Keratinocytes

Summary

An in vitro method to mimic in vivo epithelial differentiation is described. Many viruses target epithelial cells as part of their viral life cycle, and this method provides a means of examining virus:host interactions that more closely resembles that which occurs in vivo. This technique can be used with primary keratinocytes, established cell lines, as well as normal or diseased biopsy tissue.

Abstract

The development of organotypic epithelial raft cultures has provided researchers with an efficient in vitro system that faithfully recapitulates epithelial differentiation. There are many uses for this system. For instance, the ability to grow three-dimensional organotypic raft cultures of keratinocytes has been an important milestone in the study of human papillomavirus (HPV)¹. The life cycle of HPV is tightly linked to the differentiation of squamous epithelium². Organotypic epithelial raft cultures as demonstrated here reproduce the entire papillomavirus life cycle, including virus production^3,4,5. In addition, these raft cultures exhibit dysplastic lesions similar to those observed upon in vivo infection with HPV. Hence this system can also be used to study epithelial cell cancers, as well as the effect of drugs on epithelial cell differentiation in general. Originally developed by Asselineau and Prunieras⁶ and modified by Kopan et al.⁷, the organotypic epithelial raft culture system has matured into a general, relatively easy culture model, which involves the growth of cells on collagen plugs maintained at an air-liquid interface (Figure 1A). Over the course of 10-14 days, the cells stratify and differentiate, forming a full thickness epithelium that produces differentiation-specific cytokeratins. Harvested rafts can be examined histologically, as well as by standard molecular and biochemical techniques. In this article, we describe a method for the generation of raft cultures from primary human keratinocytes. The same technique can be used with established epithelial cell lines, and can easily be adapted for use with epithelial tissue from normal or diseased biopsies⁸. Many viruses target either the cutaneous or mucosal epithelium as part of their replicative life cycle. Over the past several years, the feasibility of using organotypic raft cultures as a method of studying virus-host cell interactions has been shown for several herpesviruses, as well as adenoviruses, parvoviruses, and poxviruses⁹. Organotypic raft cultures can thus be adapted to examine viral pathogenesis, and are the only means to test novel antiviral agents for those viruses that are not cultivable in permanent cell lines.

Protocol

1. Preparation for Organotypic Raft Cultures

1. The metal raft grids much first be treated with chromic sulfuric acid to remove any residue that could interfere with the differentiation process. Immerse metal grids in a glass beaker containing sulfuric acid for one hour, then continuously rinsed overnight with tap water. After the overnight rinse, raft grids should be rinsed for 3-5 hours in double distilled water.
2. To provide support for the rafts, bend three sides of the raft about 0.5 cm at equal distance from each other. The metal grids should then be autoclaved.
3. Prepare the 10X reconstitution buffer by adding 2.2 g NaHCO3 and 4.8 g Hep....

Discussion

We describe here a method that can be used to study epithelial differentiation in general, but can also easily be adapted to study viral pathogenesis, as well as the efficacy of potential therapeutics. Many viruses target epithelial cells either as the primary site of infection, as in the case of HPV, or at some point in the viral life cycle, as with herpesviruses. Although growing organotypic raft cultures is time consuming, the ability to faithfully recapitulate in vivo epithelial differentiation provides an e.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Rat Tail Collagen type 1 (4-5mg/ml)	BD Biosciences	354236
DMEM without NaHC03	Invitrogen	12100-061
NaHC03	Sigma-Aldrich	S5761
Hepes	Calbiochem	391338
Stainless Steel metal grids	Williams and Mettle Co.	CR-03063-040-100-S
E medium11
Epidermal Growth Factor	BD Biosciences	354010