Table 2.
Comparison of milky spots (MS) and fat-associated lymphoid clusters (FALCs).
| Feature | MS | FALCs |
|---|---|---|
| Location | Greater omentum | Mesenteric, mediastinal gonadal, and pericardial fat (19, 24, 25) |
| Size | 349–756 µm in diameter in humans (26). 850 µm in diameter in healthy rabbits (27) | 100–500 µm in diameter in mice (19). Size tends to increase with age (28) |
| Cell composition | Macrophages (47.5%) | B lymphocytes |
| B lymphocytes (29.1%) | T lymphocytes | |
| T lymphocytes (11.7%) | Macrophages | |
| Mast cells (6.1%) (26) | ||
| Type 2 innate lymphoid cells (ILC2) (19) | ILC2 (20–40%) (19) | |
| CXCL13+ and FDCM1+ stromal cells (29, 30) | CXCL13+ stromal cells (24) | |
| Developmental requirements | MS develop independently of ILC3/LTi cells and the chemokines CCL19 and CCL21. On the other hand, MS are defective or absent in Cxcl13−/− and Ltα−/− mice (30) | FALCs develop independently of ILC3/LTi cells and LTβR signaling. In contrast, their development is dependent on TNF signaling on stromal cells. IL-4R signaling and the presence of invariant natural killer T cells are also required. The requirement for type 2 ILCs in FALC development remains to be investigated (24) |
| Ontogeny | Accumulation of myeloid cells in the greater omentum has been observed at 20 weeks of gestation. True MS are observed at 35 weeks of gestation in humans (31) | Mesenteric FALCs are formed after birth, with visible clusters at 2–3 weeks of age in mice (24) |