help with some biology questions please

There are two questions in my biology assignment which seems tricky to me, since I have no background:

1. Which of the following two is wrong?

helper T lymphocytes: Stimulate the differentiation and proliferation of B cells and T cells.
dendritic cells: express CD4 and CD8 molecules on the surface.

2. I know IgA is the first line of defense against pathogenic antigens, but IgM is produced first when an antigen is introduced, right? Does IgM count as the first line of defense too?

Thanks

oh god were any of those words