CXCL13 expression in HIV-1⁺ lymph nodes. Immunohistochemical detection of CXCL13 expression (brown) on paraffin sections and characterization of the positive cells (blue). Slides were viewed with a Zeiss AxioImager M1 microscope for brightfield and fluorescence application (Carl Zeiss, Jena, Germany) using Plan-NEOFLUAR lens at 20×/0.5 and 63×/1.3 oil objective. Images were acquired using AxioCam MRc5 camera (Zeiss) and Axio-Vision (release 4.6) software. Digitalized images were processed with the Module Imaging Plus (Zeiss) and Adobe Photoshop version CS3 Extended software (Adobe Systems, San Jose, CA). Original magnifications, panels A and D, ×80; panels B and C, ×160. (A) In the GC light zone, part of the follicular DC network stained positive for CXCL13. (B) In HIV-1⁺ tissue, double-positive cells (CXCL13⁺CD79a⁺), B cells could be detected. (C) The majority of CXCL13⁺ cells were found in the T-dependent zone, and double-staining showed that cells were CD68⁺ macrophages, (D) but that the majority of double-positive cells were CD1a⁺ immature DCs.