NBME 12 question

[thecalccobra]

45 year old man allergic to grass pollen has basophils taken out of peripheral blood and incubated with anti-IgE Antibodies. What substance will be present after 1 minute?

a) Histamine
b) Leukotriene C4
c) Leukotriene D4
d) Major basic proteins
e) Prostaglandin D2



How is the answer A? I understand Omalizumab will bind the Fc portion of IgE, prevent the cross-linking and thus degranulation so why would histamine be present since there would be no degranulation?

Thanks.

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[oceanillusion42]

45 year old man allergic to grass pollen has basophils taken out of peripheral blood and incubated with anti-IgE Antibodies. What substance will be present after 1 minute?

a) Histamine
b) Leukotriene C4
c) Leukotriene D4
d) Major basic proteins
e) Prostaglandin D2



How is the answer A? I understand Omalizumab will bind the Fc portion of IgE, prevent the cross-linking and thus degranulation so why would histamine be present since there would be no degranulation?

Thanks.

Omalizumab binds the Fc portion of mainly UNbound IgE, thus preventing the sensitizing/adherance to mast cells/basophils. This question says that the pt has a hx of allergies, and is therefore sensitized (i.e. already has IgE on basophils). Giving an anti-IgE antibody in the mixture would (I assume) cause a crosslinking of the already present IgE on the basophil and thus lead to histamine release. Omalizumab has nothing to do with this question.

That'd be my best guess anyways.