3.1. Available and suitable cell lines

Working with permanent cell lines has several advantages over working with primary cells and non-permanent cell lines. One of the major advantages is that most of these cell lines can be propagated endlessly and without any restriction in the quantity of cells available for experiments. It may take several weeks to have hundreds of flasks with confluent cell layers, but it is possible to obtain them. In contrast, the establishment of primary cells and non-permanent cell lines depends on the availability of the organisms or organs used for cell isolation and the amount of cells depends on the size of the organ and the survival rate of the dissociated cells once they are in culture.

In addition, permanent cell lines are advantageous when experiments need standardized conditions or when experiments need to be performed or reproduced at different locations. Reproducibility is much more difficult with primary cells and non-permanent cell lines. Even if the involved groups follow the very same protocol, they will have to use different animals for cell isolation, which might lead to deviation in results. A recent publication described the alleged immortalization of honey bee embryonic cells by gene transfer of the human c-myc proto-oncogene (Kitagishi et al., 2011). Although this might be the first permanent honey bee cell line, this cell line can only be considered “of honey bee character” due to the expression of a central transcription factor of human origin known to change the entire cellular program by unregulating the expression of many genes (Nasi et al., 2001; Pelengaris and Khan, 2003). Therefore, working with permanent cell lines in honey bee research is equivalent to working with heterologous (isolated from lepidopteran or dipteran insects or else) or aberrant (in vitro transformed) cell lines and special experimental precautions are necessary. Experiments need to be thoroughly conducted, and proper controls need to be included to avoid cell culture artifacts or artifacts due to the heterologous system. A list of cell lines which proved to be useful heterologous models in bee pathology (Gisder et al., 2011) is given in Table 2. Which heterologous cell line is the best for the planned experimental approach needs to be tested by each researcher.

Table 2. List of commercially available, permanent cell lines established from lepidopteran or dipteran insects suitable for certain applications in honey bee research.

cell line

source organism

source tissue

cell morphology*

IPL-LD-65Y

Lymantria dispar

larval tissue

Large cells ; up to 30% grow adherent with processes ; suspension cells are round to oval

MB-L2

Mamestra brassicae

larval tissue

Polymorphic round cells, partly adherent

MB-03

Mamestra brassicae

larval tissue

Polymorphic round cells, partly adherent

MB-L11

Mamestra brassicae

larval tissue

Polymorphic round cells, partly adherent

Schneider-2

Drosophila melanogaster

late embryo

Small adherent cells growing in monolayers, a small number of cells is also in suspension

Sf-9

Spodoptera frugiperda

pupal ovarian tissue

Polymorphic round cells, partly adherent

Sf 21

Spodoptera frugiperda

immature ovaries

90% round cells, 10% spindle shaped, adherent

Sf-158

Spodoptera frugiperda

pupal ovarian tissue

Polymorphic round cells, partly adherent

SPC-BM-36

Bombyx mori

larval tissue

Large, mostly adherent cells ; 90% round cells (singly or aggregates), 10% spindle-shaped cells with long processes

Tn-368

Trichoplusia ni

larval tissue

Spindle-shaped cells growing in suspension (90%) ; cells tend to cluster in aggregates