Age-Dependent Changes in Ki-67 And Bcl-6 Immunohistochemical Expression in Rat Lymph Nodes Under Combined Inhalational Exposure to Pm2.5 And Tobacco Smoke and Their Biocorrection

Abstract

Background. Ambient fine particulate matter (PM2.5) and tobacco smoke are two of the leading global risk factors, and their combined inhalation damages the adaptive immune system; however, the age-dependent germinal-centre response of regional lymph nodes to such combined exposure, and its correction, are poorly characterized.

Aim. To quantify the proliferative (Ki-67) and germinal-centre B-cell (BCL-6) immunohistochemical profile of tracheobronchial and mediastinal lymph nodes in rats of three ages (6, 12 and 18 months) under combined PM2.5 + tobacco-smoke exposure and after biocorrection with an infusion of Althaea officinalis L. Methods. Ki-67 and BCL-6 were assessed by HRP–DAB immunohistochemistry with digital quantification in QuPath v0.6.0 and semiquantitative IRS (Remmele–Stegner) scoring in control, combined-exposure and biocorrection groups. The recovery rate was defined as (biocorrection − exposure)/(control − exposure) × 100%.

Results. In control animals both markers declined physiologically with age (Ki-67 68→61→54%; BCL-6 24→18→12%). Combined exposure reduced Ki-67 by 47.1%, 52.5% and 59.3% and BCL-6 by 54.2%, 55.6% and 58.3% relative to age-matched control, deepening with age. Biocorrection restored Ki-67 to 59/51/43% and BCL-6 to 20/15/10%, with recovery rates of 71.9/68.8/65.6% (Ki-67) and 69.2/70.0/71.4% (BCL-6). The immunohistochemical changes paralleled the morphometric germinal-centre reduction. Conclusion. Combined PM2.5 + tobacco-smoke exposure produces a cumulative, age-aggravated “Ki-67↓ + BCL-6↓” suppression of germinal-centre proliferative and B-cell function, and Althaea officinalis exerts a marked but incomplete, protective and functionally restorative (immunomodulatory) effect rather than absolute regeneration.

Keywords:

Lymph node, germinal centre, Ki-67, BCL-6

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