A possible mechanism for this gender-based discrepancy is a difference in the expression of the HIV virion target on T-cells (CCR5 co-receptor) in women versus men. Portales and others have demonstrated a lower membrane density of CCR5 in women, which they postulate may be caused by the inhibitory effects of progesterone on CCR5 expression.(12) Because the membrane density of CCR5 determines the in vitro infectability of a target cell by an HIV-1 R5 strain, this finding could account for the gender difference seen in HIV-1 viral loads. Thus, clinicians caring for the HIV-infected woman should probably emphasize CD4 T cell count over viral load when making decisions about initiating HIV treatment.
This, in itself, does not mean that your health store progesterone cream is a cure for immune deficiency, yet it is fascinating to think that a natural hormone could potentially play an important role in holding back this intractable disease.
Here is another reference to the findings by Portales which notes lower viral loads and ccr5 expression in women and finds progesterone the most likely factor in the discrepancy.