Rabbit macrophages secrete two biochemically and immunologically distinct endogenous pyrogens

Area of Science:

• Immunology
• Biochemistry

Background:

• Endogenous pyrogens mediate fever responses.
• Rabbit endogenous pyrogens were previously characterized into distinct groups.

Purpose of the Study:

• To differentiate between rabbit endogenous pyrogens based on their biochemical and immunological properties.
• To investigate the structural and functional differences between pyrogen forms.

Main Methods:

• Isoelectric focusing (pI) to separate pyrogen forms.
• Antisera neutralization assays to assess immunological relatedness.
• Chemical modification (N-ethylmaleimide, iodoacetamide) and affinity chromatography (Thiol-Sepharose) to probe for sulfhydryl groups.
• Limulus lysate test for endotoxin contamination.

Main Results:

• Two distinct groups of rabbit endogenous pyrogens were identified: one with pI 7.3 and another family with pI 4.5-5.0.
• Antisera neutralized the pI 7.3 pyrogen but not the pI 4.5-5.0 pyrogens.
• The pI 7.3 pyrogen possessed an essential free sulfhydryl group, indicated by inactivation with thiol-reactive agents and binding to Thiol-Sepharose.
• The pI 4.5-5.0 pyrogens lacked free sulfhydryl groups and were not affected by thiol-reactive agents or Thiol-Sepharose.
• All pyrogen forms tested negative for bacterial endotoxins.

Conclusions:

• Rabbit endogenous pyrogens with pI 7.3 and pI 4.5-5.0 represent distinct molecular entities.
• The pI 7.3 pyrogen is likely a thiol-containing protein, while the pI 4.5-5.0 pyrogens are structurally different.
• These findings suggest limited or no evolutionary or functional relationship between the identified pyrogen groups.