Table 1.

Categories of virus–virus interaction.

I. Direct interactions

a. Helper-dependent viruses

b. Pseudotype viruses

c. Superinfection exclusion

d. Genomic recombination

e. Embedded viruses

f. Heterologous transactivation

II. Environmental interactions

a. Indirect transactivation of genes

b. Breakdown of physical barriers

c. Altered receptor expression

d. Heterologous activation of pro-drugs

e. Modification of the interferon-induced antiviral state

III. Immune effects

a. Altered immune cell activation

b. Induction of autoimmunity

c. Antibody-dependent enhancement of infection

d. Heterologous immunity