[Retroviruses and the development of lymphoma].

Retroviruses are small, RNA-containing enveloped viruses which are widely distributed in nature. They exist in many animal species as well as in man. Exogenous virus strains are horizontally transmitted between individuals of a given species, like all other virus groups. Endogenous virus strains have managed some time during evolution to infect germ line cells like oocytes and spermatocytes and are thus transmitted vertically from parents to offspring. Several retrovirus strains possess oncogenes, i.e., acutely tumor-inducing genes. There are four human retrovirus strains so far. The initially discovered strain, HTLV-I, is accepted to be a co-factor in the development of an acute T-cell leukemia in adults. HTLV-II has repeatedly been isolated from cells of patients with hairy cell leukemia. Its etiological significance is unclear at present. HTLV-III/LAV-1, now designated HIV-1, is the causative agent of AIDS. HTLV-IV and LAV-2 are additional HIV-1 related strains and are supposed to cause AIDS as well. What is known about the pathogenicity of the human retrovirus strains will be discussed.