An Immunodeficient Mouse Strain Is Identified, That Has a Single $\beta$

An immunodeficient mouse strain is identified, that has a single gene defect causing its disease. Mice with this defect have greatly impaired responses to protein antigens following subcutaneous immunization and also exhibit severely delays in the kinetics of their antibody responses. Analysis of their lymph nodes revealed profound alterations in the normal architecture, with a lack of organization of distinct T-cell and B-cell zones. A likely candidate for the defect in these mice is:

A) The chemokine receptor CCR7, which recruits B cells, T cells, and dendritic cells to lymph nodes.
B) The TNF family member LT- $\beta$ , which is made by Lti cells.
C) The chemokine receptor CXCR5 that recruits B cells to the lymph node follicles.
D) Prox1, the transcription factor required for the development of lymphatic vessels.
E) TNF- $\alpha$ , which is required for the development of FDCs.