IN-VIVO EVIDENCE FOR A NON-T CELL ORIGIN OF INTERLEUKIN-5

Eosinophil myelopoiesis is to a great extent regulated by interleukin (IL)-5. Analysis of IL-5 mRNA in spleen cell preparations by reverse t ranscription-polymerase chain reaction (RT-PCR) revealed the presence of message for this cytokine in uninfected severe combined immunodefic iency (SCID) mice. This message was increased following Mycobacterium avium infection. Normal BALB/c mice had higher levels of expression of IL-5 but the expression of this cytokine was reduced during M. avium infection. Anti-IL-5 monoclonal antibody administration in vivo to SCI D mice reduced the number of peritoneal and splenic eosinophils. Gamma interferon (IFN-gamma) had an inhibitory effect of eosinophilopoiesis during infection of SCID mice by M. avium since neutralization of thi s cytokine increased the number of eosinophils detected in the periton eal cavity of infected animals. Our results suggest that IL-5 may be p roduced by cells other than T cells that are both able to respond to i nfection and are under the control of IFN-gamma.