"We encourage you to share this information with your fans and followers, and become an agent of truth and change," the letter says.
Illinois is the second state to completely reverse its HIV criminalization laws. Texas did so in 1994.
Among numerous offensive statements, the rapper said those with HIV live only a few weeks.
The bar has sold out of the shirts with the hateful message.
The launch of the My Body, My Health leads up to National HIV Testing Day on June 27.
The man had told people at a party that he was living with HIV.
Experts say increased funding for HIV services and prevention and fighting stigma are key.