Modification of immunologic and hematologic variables by method of CO2 euthanasia.
OBJECTIVE
The major goal was to determine whether variations in the method of CO2 euthanasia would induce significant immunologic differences.


METHODS
Young adult C57BL/6 mice (n = 40) were euthanized, using four regimens: 70% CO2/30% O2; 70% CO2/30% O2-->100% CO2; 100% CO2-naïve chamber; and 100% CO2 pre-charged chamber. Time to recumbency and euthanasia and body, liver, lung, spleen, and thymus masses were determined. Blood and spleen were further evaluated for leukocyte, lymphocyte, and thrombocyte counts, erythrocyte characteristics, distribution of lymphocyte subpopulations, spontaneous and mitogen-induced blastogenesis, complement activity, and cytokine production.


RESULTS
Time to euthanasia was five- to eightfold longer in mice exposed to 70% CO2/30% O2 than that for any other group. There were slight increases in mean erythrocyte volume (MCV) and mean erythrocyte hemoglobin (MCH) for all groups, compared with those for the 100% CO2 pre-charged group. Circulating cytotoxic T (CD8+) lymphocyte percentages and numbers, and spontaneous blastogenesis of leukocytes in blood and spleen, also were affected by euthanasia method.


CONCLUSIONS
The method of CO2 euthanasia can result in significant differences in immunologic/hematologic variables. Thus, consistency in euthanasia procedures may be important in accurate interpretation of research data.
Pecaut
M J
MJ
Department of Radiation Medicine, Loma Linda University, CA 92354, USA.
Smith
A L
AL
Jones
T A
TA
Gridley
D S
DS
D000818:Animals; D001772:Blood Cell Count; D002245:Carbon Dioxide; D003165:Complement System Proteins / Q000502:physiology; D016207:Cytokines / Q000032:analysis; D005065:Euthanasia / Q000662:veterinary; D005260:Female; D007958:Leukocyte Count; D008213:Lymphocyte Activation; D018655:Lymphocyte Count; D008214:Lymphocytes / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009929:Organ Size; D010976:Platelet Count; D013997:Time Factors
D016207:Cytokines; D002245:Carbon Dioxide; D003165:Complement System Proteins