Background: Appendixes removed from patients with suspected appendicitis often appear normal on histological examination. We examined appendix specimens for expression of abnormal amounts of cytokines, an indicator of an inflammatory response.
Methods: Tumour necrosis factor alpha (TNFalpha) and interleukin-2 (IL-2) expression was measured by in-situ hybridisation in ten specimens from patients with acute appendicitis, 12 normal appendix specimens removed from patients undergoing elective abdominal surgery, and 31 appendix specimens from patients with a clinical diagnosis of appendicitis but an appendix histologically classified as normal. Cytokine-specific RNA antisense probes were prepared by in-vitro transcription and digoxigenin (DIG) labelled. In-situ hybridisation was done on 5 micrometer paraffin sections. Tissue sections hybridised by sense probes acted as negative control for each cytokine. Following hybridisation, the probes were detected by alkaline phosphatase labelled anti-DIG monoclonal antibody and visualised by nitroblue tetrazolium staining.
Findings: All histologically proven acute appendicitis specimens demonstrated intense cellular TNFalpha mRNA expression in germinal centres and moderate levels of expression throughout the mucosa. IL-2 mRNA was strongly expressed in the lamina propria and only moderately expressed in germinal centres. Normal appendixes all showed almost complete absence of TNFalpha and IL-2 mRNA expression. Seven of the 31 histologically classified normal appendix specimens from patients with a clinical diagnosis of appendicitis demonstrated TNFalpha and IL-2 mRNA expression similar to acute appendicitis specimens in germinal centres, submucosa, and lamina propria layers.
Interpretation: TNFalpha and IL-2 mRNA expression is a sensitive marker of inflammation in appendicitis. A substantial proportion of histologically normal appendixes showed clear evidence of an inflammatory response in the form of increased cytokine expression.