Morphological and immunological evidence of a unique selective production and endoplasmic reticular accumulation of interleukin-1α in rat peritoneal macrophages induced by Pseudomonas aeruginosa exotoxin A

The immunotoxicity of Pseudomonas aeruginosa exotoxin A (ETA) on macrophages was evaluated by incubating rat peritoneal macrophages (RPM) with 1–100 ng/ml ETA for 3–60 h. Although the overall changes in cell viability and DNA, RNA, and protein synthesis of the ETA-treated RPM (E-RPM) were reduced in a dose- and time-dependent manner, there was a transient but evident rebound in RNA and/or protein synthesis at 24–36 h post-incubation (HPI) at 1–50 ng/ml ETA. However, a more apparent enhancement appeared in RNA and protein synthesis at 36–48 HPI in 10 and 50 ng/ml E-RPM after normalized on the basis of viable cell. Most 50–100 ng/ml E-RPM underwent necrosis/apoptosis before 24 HPI. By 36 HPI, 41% of 10 ng/ml E-RPM remained viable but were full of cytoplasmic granules due to the accumulation of glycoprotein in segmentally dilated endoplasmic reticulum. Immunological staining of the granules revealed strong IL-1α but weak or no signals for IL-1β, IL-1 receptor antagonist, IL-6, and TNF-α. A time-dependent increase in IL-1α but no IL-1β was detected in cell lysate of 10 ng/ml E-RPM; however, neither IL-1α nor IL-1β was detected in culture supernatant. Thus, besides cytopathic and functional effects, ETA could induce a unique selective production and endoplasmic reticular accumulation of IL-1α in RPM.