Gillin F D, Reiner D S, Gault M J
Infect Immun. 1985 Mar;47(3):619-22. doi: 10.1128/iai.47.3.619-622.1985.
We showed previously that nonimmune human milk (NHM) kills Giardia lamblia trophozoites in vitro and presented evidence that killing requires the bile salt-stimulated lipase of milk. Since this enzyme is activated by bile salts, killing should be dependent on the presence of bile salts. We now show that killing by fresh NHM or NHM stored at -70 degrees C is totally dependent on sodium cholate (a bile salt). With less than 0.4 mM cholate, no parasites were killed, whereas with 1 mM cholate, greater than 99.7% were killed by 5% NHM in 30 min. Moreover, killing activity was completely heat labile. The G. lamblia-killing activity of human milk was greatly altered by storage at -10 or -20 degrees C. In less than 23 days, the 50% lethal dose decreased, cholate dependence was lost, and killing activity became heat stable. In contrast, the activity of milk stored at -70 degrees C remained unchanged. Milk lipase activity, like killing activity, became cholate independent during storage at -10 or -20 degrees C. On the basis of these results, we hypothesize that killing of G. lamblia by fresh NHM or NHM stored at -70 degrees C depends on bile salt-stimulated lipase, which must be activated by bile salts. In contrast, NHM stored at -20 degrees C accumulated free fatty acids which kill G. lamblia. In support of this thesis, milk stored at -10 degrees C had a concentration of 18.7 mM free fatty acids compared with only 1.1 mM in an identical sample stored at -70 degrees C.
我们之前的研究表明，非免疫性人乳（NHM）在体外可杀死蓝氏贾第鞭毛虫滋养体，并提供证据表明这种杀伤作用需要乳汁中胆盐刺激的脂肪酶。由于该酶由胆盐激活，因此杀伤作用应依赖于胆盐的存在。我们现在发现，新鲜的NHM或储存在-70℃的NHM的杀伤作用完全依赖于胆酸钠（一种胆盐）。胆酸盐浓度低于0.4 mM时，没有寄生虫被杀死；而胆酸盐浓度为1 mM时，5%的NHM在30分钟内可杀死超过99.7%的寄生虫。此外，杀伤活性完全不耐热。人乳对蓝氏贾第鞭毛虫的杀伤活性在-10℃或-20℃储存时会发生很大变化。在不到23天的时间里，50%致死剂量降低，对胆酸盐的依赖性丧失，杀伤活性变得耐热。相比之下，储存在-70℃的乳汁活性保持不变。在-10℃或-20℃储存期间，乳脂肪酶活性与杀伤活性一样，变得不依赖于胆酸盐。基于这些结果，我们推测新鲜的NHM或储存在-70℃的NHM对蓝氏贾第鞭毛虫的杀伤作用依赖于胆盐刺激的脂肪酶，而该酶必须由胆盐激活。相比之下，储存在-20℃的NHM会积累游离脂肪酸，这些游离脂肪酸可杀死蓝氏贾第鞭毛虫。为支持这一论点，储存在-10℃的乳汁中游离脂肪酸浓度为18.7 mM，而储存在-70℃的相同样本中仅为1.1 mM。
