Protection against reticuloendotheliosis virus—strain T tumours is associated with JMV‐1 culture supernatant‐enhanced natural killer cell activity

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Abstract
One‐day‐old chicks were inoculated intraperitoneally with cell‐free JMV‐1 culture supernatant and were subsequently challenged with a lethal dose of RECC‐CU60 tumour cells at either 7 or 12 days of age. A significant reduction in mortality was evidenced in chicks that had been inoculated with JMV‐1 culture supernatant prior to RECC‐CU60 tumour cell challenge at 12 days of age, compared with all other treatment groups. Reducing the serum content of JMV‐1 culture medium or changing the base medium in which the JMV‐1 cells were grown did not affect the reduction in mortality, demonstrating that the protective effects against RECC‐CU60 tumour cell challenge were a result of factors secreted into the culture medium by JMV‐1 cells. Development of natural killer (NK) cell activity correlated with findings in the RECC‐CU60 tumour cell challenge studies. Inoculation of 1‐day‐old chicks with JMV‐1 culture supernatant resulted in a significant increase in NK cell activity in spleens taken from JMV‐1 inoculated chicks 12 days later, when compared with spleens taken from chicks in all other treatment groups. Inoculation of chicks with RECC‐CU60 tumour cells caused a suppression of their NK cell activity. Treatment of chicks with JMV‐1 supernatant at day of age, prior to RECC‐CU60 tumour cell challenge restored and significantly enhanced their NK cell activity. These results suggest that the JMV‐1 cell line secretes lymphokines that protect against RECC‐CU60 tumour cell challenge by directly or indirectly stimulating NK cell activity.