• Young child with non-reactive skin testing for multiple antigens (which is a type 4 hypersensitivity process dependent upon T cells), raising concern for T lymphocyte dysfunction
• Key idea: Patients with HIV can have a falsely-negative PPD in the setting of M. tuberculosis because they have low T cell function and impaired Type 4 HS reaction
• Antibody deficiency = Bruton’s agammaglobulinemia = Recurrent infections with encapsulated infections
• Complement deficiency = Recurrent Neisseria infections
• Impaired chemotaxis = Leukocyte adhesion deficiency = Recurrent abscesses without pus, delayed wound healing, delayed umbilical cord separation
• Impaired respiratory burst = chronic granulomatous disease = Recurrent skin abscesses and infections with catalase positive organisms (Staph, Pseudomonas, Aspergillus, Nocardia, Serratia, etc.)
• Splenic dysfunction (sickle cell disease, trauma patient) = Encapsulated infections (Strep pneumo, H. influenzae, Neisseria)

. The immune response to M tuberculosis is T cell dependent. It comprises not only the conventional CD4 and CD8 T cells, but also γδ T cells and CD1 restricted T cells. γδ T cells recognise phospholigands and no presentation molecules are known thus far. CD1 restricted T cells recognise glycolipids, which are highly abundant components of the mycobacterial cell wall. Although different T cells are required for optimum protection, the immune mechanisms known to have a role in acquired resistance can be associated with two major mechanisms: (a) activation of macrophages by cytokines; (b) direct cytolytic activity. In vivo granuloma formation, which is central to protection, is induced and sustained by cytokines. Mycobacteria are contained within granulomas and in this way are prevented from spreading all over the body.

So it looks like we just need to know this. Nevermind the fact the question stem doesnt even hint at any congenital problem in the girl....

"The response is a classical example of delayed-type hypersensitivity reaction (DTH), a type IV of hypersensitivities. T cells and myeloid cells are attracted to the site of reaction in the timeframe of 1-3 days and generate local inflammation." - Wikipedia