Received 6/18/97, Accepted 7/22/97

We hypothesize that the protective natural defenses against a specific group of retrovirus and genetically-closely-related viruses would be life long unless untoward events or cofactors adversely affected the anti-retroviral "molecular immunity" by inducing alterations in the subsets of lymphocytes that are involved in molecular immunity (i.e CD8+ cells). These cofactors are especially important during the initial stages of infection, at which time they can determine the future course of infection. "Untoward events or cofactors" are of several types, including exposure to low-dose radiation, UV-light, cyclophosphamide and protein-synthesis inhibitors (118). Another type of cofactor is co-infection with another pathogenic virus or exposure to specific viral products—these other viruses need not necessarily be retroviruses (reviewed in 118). A third type of cofactor is temporary immunoincompetence due to abuse of certain substances, such as alcohol (119-123), cocaine (124-127) or even certain anti-HIV-1 drugs (118)—these latter cofactors may be of particular significance during the initial exposure (118). No doubt there are also, yet unknown cofactors, which may interfere or inactivate the "molecular immunity" pathways, which will render the host susceptible to acute infection of retroviruses.