HISTOTYPIC CULTURES

Using histotypic culture, it is possible to use dispersed monolayers to regenerate tissue like structures. It the growth and propagation of cell lines in three-dimensional matrix to high cell density that contributes to this. The techniques used in histotypic cultures are:

(a) Gel and sponge technique- In this method, the gel (collagen) or sponges (gelatin) are used which provides the matrix for the morphogenesis and cell growth. The cells penetrate these gels and sponges while growing.

(b) Hollow fibers technique- In this method, hollow fibers are used which helps in more efficient nutrient and gas exchange. In recent years, perfusion chambers with a bed of plastic capillary fibers have been developed to be used for histotypic type of cultures. The cells get attached to capillary fibers and increase in cell density to form tissue like structures.

(c) Spheroids – The re-association of dissociated cultured cells leads to the formation of cluster of cells called spheroids. It is similar to the reassembling of embryonic cells into specialized structures. The principle followed in spheroid cultures is that the cells in heterotypic or homotypic aggregates have the ability to sort themselves out and form groups which form tissue like architecture. However, there is a limitation of diffusion of nutrients and gases in these cultures.

(d) Multicellular tumour spheroids- These are used as an in vitro proliferating models for studies on tumour cells. The multicellular tumour spheroids have a three dimensional structure which helps in performing experimental studies related to drug therapy, penetration of drugs besides using them for studying regulation of cell proliferation, immune response, cell death, and invasion and gene therapy. A size bigger than 500 mm leads to the development of necrosis at the centre of the MCTS. The monolayer of cells or aggregated tumour is treated with trypsin to obtain a single cell suspension. The cell suspension is inoculated into the medium in magnetic stirrer flasks or roller tubes. After 3-5 days, aggregates of cells representing spheroids are formed. Spheroid growth is quantified by measuring their diameters regularly. The spheroids are used for many purposes. They are used as models for a vascular tumour growth. They are used to study gene expression in a three-dimensional configuration of cells. They are also used to study the effect of cytotoxic drugs, antibodies, radionucleotides, and the spread of certain diseases like rheumatoid arthritis.