Focal necrosis and syncytial formation within lymph nodes was identified, together with glomerulitis
and syncytial cell formation in the kidney.
 mPSL, PEX, IVIG, Rit Stable Our case mPSL improved Diffuse infiltration of PCAR was defined as score i3 in Banff classification or described as "Diffuse." By contrast, less than i2 was described as "Focal." ND: no data; VR: vascular rejection; RTx: renal transplantation; TG: transplant glomerulitis
; DSA: donor-specific antibody; ABMR: antibody-mediated rejection; mPSL: methylprednisolone; PEX: plasma exchange; IVIG: intravenous immunoglobulin; Rit: Rituximab; OKT3: Muromonab-CD3; DSG: deoxyspergualin.
There was no significant glomerulitis and capillary loops appeared normal, without duplication.
A proportion of isolated v1 lesions may be associated with donor specific antibodies (DSA), transplant glomerulopathy, arteriosclerosis, glomerulitis, or C4D positivity suggesting that isolated v1 lesions in some cases may represent antibody-mediated rejection [11, 12].
A second biopsy was performed and it showed an acute active type 2 AMR with lesions of TMA, peritubular capillaritis, and glomerulitis (negative Cd4) associated with a grade IA cellular rejection (Figure 1).
In our case, the diagnosis of AMR was not done initially despite the presence of glomerulitis and peritubular capillaritis because C4d-negative AMR was not a recognized entity before 2014.
Caption: Figure 1: Kidney biopsy findings: (a) transplant glomerulitis with infiltrating mononuclear inflammatory cells within the capillary loops, second biopsy (PAS, magnification x200); (b) glomerulus with a thrombus involving the vascular pole, second biopsy (Jones, magnification x200); (c) glomeruli showing persistent transplant glomerulitis and thrombotic microangiopathy, fourth biopsy (PAS, magnification x100); (d) immunofluorescence microscopy showing C4d mesangial deposition without peritubular capillary staining (magnification x100).
Recently the concept of C4d negative antibody mediated rejection has been proposed, which recognises that C4d staining is problematic and proposes a new classification which includes evidence of allograft injury based on light microscopic features of glomerulitis
(Banff "g" lesions) and peritubular capillitis ("ptc" lesions).
Since PTCitis (ptc) and glomerulitis (g) are often associated with ABMR and g + ptc = 0 was confirmed to be a useful diagnostic algorithm for TCMR exclusion , we excluded all the recipients with PTCitis and glomerulitis in TCMR group.
Our previous study showed that T-bet expression is correlated with glomerulitis in ABMR, further study revealed that both glomerulitis and PTCitis are correlated with T-bet expression in TG, which is a chronic form of ABMR.
We compared the characteristics of C4d-positive ABMR and C4d-negative ABMR (Table 3) and found that there were no differences between two groups in clinical and histological characteristics, such as incidences of HLA-I/II antibodies, incidence and severity of PTC inflammation as well as glomerulitis, and most importantly, the resistance of steroid treatment.
T-bet expression is strongly correlated with peritubular capillaritis and glomerulitis, which are typical lesions of ABMR.