CD4 and infection: Immunohistologic examination at day 28 post-aerosol infection revealed that F4/80+ macrophages, CD3+, CD4+ and CD8+ cells localized in perigonadal fat (Fig 3A and 3C), whereas no positive staining for myeloperoxidase (MPO) abundantly expressed in neutrophils, or for the pan B cell marker B220 was observed (Fig 3C).