Table 1.

Parameters and Values Incorporated into the Model

parameter	symbol	value	refs
HIV-1
diffusivity in CVM	Dv	1.27 µm2/sa	7a
diffusivity in semen		assume same as in CVM
viral load in semen		8.4 × 105 copies/ejaculateb	21, 22
no. of Env trimer spikes	N*	14 ± 7 (SD)	24
IgG
diffusivity in CVM	DAb	40 µm2/s	8
diffusivity in semen		assume same as in CVM
IgG concentration in CVM		variable
IgG–Env affinity	kon, koff	variable
IgG–mucin affinity	mon [M], moff	variable
ratio of DAb vs diffusivity in buffer	α	variable
vagina
surface area of lumen	SAvagina	145 cm2c	18a,b
volume of luminal CVM	VCVM	~750 µL	25
thickness of CVM layer	L	50 µmd
volume of semen	Vsemen	~3.0 mL	22
thickness of semen layer	d	200 µmd

^aThe geometrically averaged Deff for HIV was previously measured to be 0.25 µm²/s, but with a substantial fraction of viruses exhibiting more rapid mobility. For the current analysis, we used 1.27 µm²/s, which represents the top 25th percentile of virus mobility; this is in reasonable agreement with a more recent study of HIV diffusion in genital secretions.^7c

^bEstimated on the basis of a median semen volume of 3.0 mL²² and 2.8 × 10⁵ HIV-1 RNA copies/mL, which represents the upper limit of HIV-1 RNA copies/mL in seminal plasma from ref 21. This is in reasonable agreement with another report by Chakraboty et al., which estimated 5 × 10⁵ HIV-1 RNA copies/ejaculate, with a maximum of about 2 × 10⁷ HIV-1 RNA copies/ejaculate.²⁶

^cThe mean surface area of the vagina in the native state was previously estimated to be ~ 90 cm² by injection of vinyl polysiloxane casts vaginally. Alternatively, the surface area of vaginal lumen may also be inferred by the surface area of the erect penis (average ~200 cm²) assuming complete insertion into the vagina. We took the average from the two approaches.

^dCVM (L) and semen (d) thicknesses are estimated by V_CVM/SA_vagina and V_semen/SA_vagina, respectively.