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Variation of Virulence of Transplantable Leukemias of Mice on Successive Transfers into Genetically Unrelated Hosts^{* ,}

Gustavo Hoecker, Olga Pizarro, Danko Brncic and Gabriel Gasic

( Instituto de Biologia "Juan Noe," Escuela de Medicina, Universidad de Chile, Santiago, Chile)

The reciprocal transplantability of four longtransplanted lines of leukemia, A and F from strain C58 mice and G and H from strain AK mice, was studied. Of these, lines F and G were strain-specific and did not kill mice from unrelated inbred strains. A and H, however, grew and killed more than 90 per cent of the foreign hosts in the first transfer. In the second transfer a marked drop in the number of takes was observed, the degree of reduction being related to the length of residence of the leukemic cells in the foreign host used as donor for this transfer.

In a more detailed analysis, A leukemia was transplanted into mice of seven different inbred strains. Of these, 96 per cent of the AK, 86 per cent of the C3H, and 33 per cent of the Rk mice died in the first transfer. None of the A^y, BALB/c, or DBA/1 mice that were inoculated died. In the second transfer a decrease in the number of takes was observed in mice of strains AK and Rk, which was more marked in Rk mice. In C3H, on the contrary, an increase in virulence was observed, as judged from the high mortality and the shortening of the interval before death when leukemic material from these hosts was inoculated in a second transfer into C3H hosts, and into AK and C58 strain mice.

Of two experiments involving a third transfer of line A leukemia into AK hosts, one was successful, and the A line recovered the virulence observed in the first transfer to these hosts.

It is postulated that the results measure the "protective efficiency" of the different genotypes against the particular leukemias involved. Several hypotheses to explain these complex results are discussed.

^* A preliminary report of these experiments was presented to the Congress of the International Society of Hematology, Mar del Plata, Argentine, September, 1952.

Partially financed by a grant from the Rockefeller Foundation for Medical Research.

Present address: Roscoe B. Jackson Memorial Laboratory, Bar Harbor, Maine.

Received 7/21/54.