The first four stages are approximately 5 days each in duration whereas Stage V lasts for 69 days.

Stage VI duration is indeterminate and can last for many years until immunological control fails (Fig. 1). The temporal appearance of functional responses in relation to viral dynamics provides important clues about the mechanisms of immunological control. In this regard, it is also possible to discriminate between recent and chronic infections in Fiebig Stage VI using a sensitive/less-sensitive algorithm that employs a standard HIV ELISA (sensitive) and a ‘detuned HIV ELISA’ (less sensitive) that detects increasing antibody titres that emerge early after infection.[30] Hence, the detuned ELISA can discriminate individuals in the early part of Fiebig Stage VI who were recently infected versus those who are chronically infected. More recent studies show that increased levels of acute-phase proteins, such as selleck serum amyloid precursor A, are elevated as early as the eclipse phase but wane around day 20 post-T0.[31] A cytokine storm follows beginning 6 days after T0 in Fiebig

Stage II, waning around day 20 post-T0.[32] Immune complexes of HIV with either IgM or IgG appear at day 8 post-T0 and become undetectable around day 20 post-T0. Free IgG non-neutralizing antibodies to gp41 appear 13 days after T0, early in Fiebig Stage IV.[29] Free IgG non-neutralizing antibodies appear 28 days after T0, midway in Fiebig Stage IV.[29] Autologous neutralizing antibodies appear approximately at day Protease Inhibitor Library 82 post-T0, late in Fiebig Stage V, followed by neutralization insensitive viral variants around 10 days later, apparently selected by neutralization pressure (reviewed in ref. [21]).

These antibodies are narrowly specific for autologous virus with neutralization breadth increasing slowly over time thereafter.[33] Hence, there is a 55-day window between the appearance of the first free IgG antibodies that bind to gp41 or gp120 and the emergence of narrowly specific neutralizing antibodies.[21] By contrast, the first CD8+ cytotoxic T-lymphocyte (CTL) responses appear at the beginning of Fiebig Stage III, around day 20, followed by the emergence of CTL escape viruses 10 days later at Amisulpride the beginning of Fiebig Stage V, suggesting that these responses exert immunological pressure on the virus (reviewed in ref. [21]). Because there is a 60-day lag between the CD8+ CTL response and neutralizing antibody response, it has been widely accepted that post-infection control of viraemia is largely due to CTLs. This conclusion is also supported by CD8 depletion studies in NHPs.[34, 35] By contrast, in acutely HIV-infected individuals, there is evidence that antibody-mediated cellular cytotoxicity (ADCC) responses appear around day 36 post-T0, at the beginning of Fiebig Stage V, and that these responses correlate inversely with viral load.