Figure 1.

An informal classification tree for dividing all animal cell lines into invitromes based on how they interact with a specific virus. The diagram presents the range of potential interactions between a virus and cell lines, but for a particular virus, only some of these interactions might take place. Cell lines that produce virions are members of the supportive viral invitrome (left rectangle labeled with Roman numeral I), whereas cell lines that neither produce virions nor express viral genes belong to the non-supportive viral invitrome (center rectangle labeled with Roman numeral II). Cell lines that express viral genes but do not produce virions are in the partially supportive invitrome (right rectangle labeled with Roman numeral III). The supportive viral invitrome (I) can be subdivided into the lytically permissive invitrome (IA), in which cell lines produce virions in self-limiting infections, and the persistently permissive viral invitrome (IB), in which cell lines produce virions through multiple cell divisions or can be induced after multiple cell divisions to produce virions. Subdivisions of IB are chronic focal (IB1), chronic diffuse (IB2), and latent (IB3) invitromes, and are defined in the diagram. Finally, in the partially supportive viral invitrome (III), cells support the expression of viral genes but not the full viral life cycle and virion production. This group can be divided into the abortively permissive viral invitrome (IIIA), in which the cell lines become infected but the infection is aborted before virions are produced, and the persistently semi-permissive invitrome (IIIB) in which the cell lines continuously maintain viral component(s) but neither produce nor can be induced to produce virions.