In one of the first reported cases applying the ADA Amendments Act, which took effect on Jan. 1, 2009, a district court in Northern Illinois held in Horgan v. Simmons that an employee who was fired a day after disclosing his HIV-positive status to the president of his company could pursue a claim for discrimination and impermissible medical inquiry claims under the amended Americans with Disabilities Act. Citing the EEOC's proposed regulations to implement the ADA Amendments Act, the court held that HIV substantially limits a major life activity—the function of the immune system—and therefore constitutes a disability under the ADA. The court also held that the employer's inquiry into the plaintiff's medical status despite plaintiff's repeated assurances that nothing was affecting his ability to work was an "impermissible medical inquiry" under the ADA Amendments Act, which prohibits "inquiries of an employee as to whether the employee is an individual with a disability or as to the nature or severity of the disability, unless such examination or inquiry is shown to be job-related and consistent with business necessity."