IMMUNOHISTOCHEMICAL EVALUATION OF TLR-4 RESPONSE IN THE MEDIASTINAL ADIPOSE TISSUE OF PIGS NATURALLY INFECTED WITH MYCOPLASMA HYOPNEUMONIAE

Introduction: Mycoplasma hyopneumoniae (MH) is the agent of enzootic pneumonia of pigs. Toll-like receptors 4 (TLR4) binds lipopolysaccharides (LPS) of gram- bacteria. In the adipose tissue TLR4s seem to be involved in activation and support of inflammation. Materials and Methods: Mediastinal adipose tissue and lungs were sampled from 49 pigs at slaughter. Each lung lesion was MH RT-PCR evaluated. Frozen 5 μm sections of lungs were histologically evaluated with scores ranging from 0 to 4, for BALT, bronchi lumen, bronchiolar disepithelization and subacute inflammation. Frozen 5 μm sections of corresponding mediastinal adipose tissues were ABC immunohistochemically stained using commercial anti- TLR4 antibodies. The average histological lung score ranged from 0.14 to 1.98. 32 samples were RT-PCR positive and 17 negative.10 showed subacute inflammation and 22 showed MH lesions. 20 samples, 14 MH positive and 6 MH negative, were evaluated for TLR4s, using a semi-quantitative classification for spread and intensity of staining on four levels: absent, mild, medium, intensive on four, 4 magnifications fields. Results: 3 samples (2 positive), with severe pulmonary inflammation, showed an intense immunostain for TLR4 in the adipose tissue (3). 6 samples (3 positive), with mild/severe inflammation, showed medium TRL4 stain. 8 adipose tissue samples, with mild alveolar-bronchial inflammation (6 positive), showed TLR4 0 to 1. 3 adipose tissue samples were negative with lung score 1. Conclusions: Semi-quantitative analysis of the presence of TLR4s in mediastinal adipose tissue, might confirm that a more severe pulmonary inflammation shows a higher concentration of TRL4 than in mild inflammation