**Core Concept**
SLE (Systemic Lupus Erythematosus) is an autoimmune disease characterized by the presence of autoantibodies and immune complex deposition in various tissues. The deposition of immune complexes at the dermoepidermal junction is a hallmark of cutaneous lupus erythematosus.

**Why the Correct Answer is Right**
In SLE, the deposition of immune complexes at the dermoepidermal junction is primarily composed of IgG and IgM antibodies, along with complement components such as C3 and C1q. These immune complexes are formed when autoantibodies bind to self-antigens, leading to the activation of the complement system and the deposition of immune complexes in the skin. The granular pattern of deposition observed on immunofluorescence is consistent with the presence of these immune complexes.

**Why Each Wrong Option is Incorrect**
**Option A:** IgA - While IgA can be involved in autoimmune diseases, it is not the primary constituent of immune complexes in SLE.
**Option B:** IgE - IgE is primarily involved in allergic reactions and is not typically associated with immune complex deposition in SLE.
**Option C:** Complement C5b - While complement components are involved in the formation and deposition of immune complexes, C5b is not a primary constituent of these deposits.

**Clinical Pearl / High-Yield Fact**
In SLE, the presence of immune complexes at the dermoepidermal junction can be visualized on immunofluorescence as a granular pattern, which is a key diagnostic feature of cutaneous lupus erythematosus.

**Correct Answer:** C. Complement C1q.