Abstract
Hepatocyte growth factor (HGF) augments proliferation, survival and increases migration of plasma cells in vitro and in addition it induces haemangiogeneis and lymphangiogenesis. C-met (HGF receptor) is expressed on plasma cells and HGF is constitutively elevated in serum of patients with myeloma (MM) and MGUS patients. We investigated the distribution of HGF in bone marrow biopsies to better understand its role in progression of monoclonal gammopathy.
Materials and methods: Bone marrow trephines were analysed by immunohistochemistry of paraffin embedded bone marrow (BM) trephine specimens. Trephines were dewaxed without antigen retrieval. Plasma cell enumeration was done using CD38 staining (Novocastra, UK). HGF (Goat antihuman IgG, R&D systems) staining was performed using Vectastain® ABC kit with DAB reactivity. Slides were analysed using an Optical microscope (Zeiss Standard 20, Germany).
Results: Archived BM specimens of MM (n= 7), MGUS (n= 5) and normal controls (n=6) were stained in duplicate. Trephines were graded from Grade 1–3 (weak, moderate, strong) based on the intensity of staining. The localisation of staining to paratrabecular, perivascular and intertrabecular areas was analysed. Interstitial and cytoplasmic staining patterns were analysed. HGF staining localised to paratrabecular regions was observed in all normal individuals with staining intensity of Grade 1–2 in 3/6(50%) and Grade 3 in 3/6(50%). In 4/5(80%) patients with MGUS a distinct intertrabecular pattern of staining was observed in discrete regions, where plasma cells were localised. Intensity of staining was Grade 2 in 3/5(60%) and Grade 3 in 2/5(40%) MGUS patients. Plasma cell percentages were between 5–20% in MGUS patients. In MM patients we found a correlation between the plasma cell counts and the degree of HGF staining. In 2/7 (28.5%) patients plasma cell percentages ranged between 5% and 15% and Grade 1–2 discrete paratrabecular staining was observed with none or low perivascular staining. In 5/7 (71.5%) MM patients plasma cell percentages were >20% and Grade 3 confluent staining with interstitial and cytoplasmic location of HGF was observed. In addition, patients with Grade 3 staining presented a strong perivascular localisation of HGF.
Conclusion: HGF distribution in bone marrow microenvironment of MGUS and MM patients is non random. We observed that MGUS patients have a discrete intertrabecular pattern and MM patients have a confluent interstitial pattern of staining with strong perivascular localisation. Other groups have shown that high HGF levels increase angiogenesis. We hypothesise that HGF localisation and pattern of distribution in BM microenvironment leads to neo angiogenesis and progression from MGUS to MM. Ongoing studies are evaluating this hypothesis.
Author notes
Disclosure: No relevant conflicts of interest to declare.
