I am a volunteer adn not a medical professional, so my input is based on my experience in caring for my son who is now 10, but was diagnosed at age 3.
Everything I have read, says something along these lines....
"Type 1 diabetes: Type 1 diabetes, formerly called juvenile diabetes or insulin-dependent diabetes, is usually first diagnosed in children, teenagers, or young adults. In this form of diabetes, the beta cells of the pancreas no longer make insulin because the body's immune system has attacked and destroyed them. "
Here is some info. on all 3 cells you mentioned:
Alpha Cell (I do not think these are attacked because SOMETIMES when diabetics experience low BG's, there body's glucagon kicks in, thus bringing the blood sugar up)
"A type of cell in the islets of Langerhans in the pancreas that make and release a hormone (glucagon) that raises the level of glucose in the blood."
"A type of cell in the Islets of Langerhans in the pancreas that make and release insulin."
Delta Cell (I believe these are the cells that are affected in type 2, which is different than type 1 diabetes)
"A type of cell in the pancreas in areas called the islets of Langerhans. Delta cells make somatostatin, a hormone that is believed to control how the beta cells make and release insulin and how the alpha cells make and release glucagon."
Sorry I could not give a straight answer, but, to my knowledge it is the beta cells that are attacked in type 1 diabetes.
I am sure that others who visit this site, along with the other volunteers will leave additional comments to help aid in answering your question.
Thank you for posting.