Anti-CD20 antibody immunotherapy effectively treats non-Hodgkin's lymphoma and autoimmune disease. However, the cellular and molecular pathways for B cell depletion remain undefined because human mechanistic studies are limited. Proposed mechanisms include antibody-, effector cell–, and complement-dependent cytotoxicity, the disruption of CD20 signaling pathways, and the induction of apoptosis. To identify the mechanisms for B cell depletion in vivo, a new mouse model for anti-CD20 immunotherapy was developed using a panel of twelve mouse anti–mouse CD20 monoclonal antibodies representing all four immunoglobulin G isotypes. Anti-CD20 antibodies rapidly depleted the vast majority of circulating and tissue B cells in an isotype-restricted manner that was completely dependent on effector cell Fc receptor expression. B cell depletion used both FcγRI- and FcγRIII-dependent pathways, whereas B cells were not eliminated in FcR common γ chain–deficient mice. Monocytes were the dominant effector cells for B cell depletion, with no demonstrable role for T or natural killer cells. Although most anti-CD20 antibodies activated complement in vitro, B cell depletion was completely effective in mice with genetic deficiencies in C3, C4, or C1q complement components. That the innate monocyte network depletes B cells through FcγR-dependent pathways during anti-CD20 immunotherapy has important clinical implications for anti-CD20 and other antibody-based therapies.

CD20 mAb-mediated B cell depletion is an effective treatment for B cell malignancies and some autoimmune diseases. However, the full effects of B cell depletion on natural, primary, and secondary Ab responses and the maintenance of Ag-specific serum Ig levels are largely unknown. The relationship between memory B cells, long-lived plasma cells, and long-lived humoral immunity also remains controversial. To address the roles of B cell subsets in the longevity of humoral responses, mature B cells were depleted in mice using CD20 mAb. Peritoneal B cell depletion reduced natural and Ag-induced IgM responses. Otherwise, CD20+ B cell depletion prevented humoral immune responses and class switching and depleted existing and adoptively transferred B cell memory. Nonetheless, B cell depletion did not affect serum Ig levels, Ag-specific Ab titers, or bone marrow Ab-secreting plasma cell numbers. Coblockade of LFA-1 and VLA-4 adhesion molecules temporarily depleted long-lived plasma cells from the bone marrow. CD20+ B cell depletion plus LFA-1/VLA-4 mAb treatment significantly prolonged Ag-specific plasma cell depletion from the bone marrow, with a significant decrease in Ag-specific serum IgG. Collectively, these results support previous claims that bone marrow plasma cells are intrinsically long-lived. Furthermore, these studies now demonstrate that mature and memory B cells are not required for maintaining bone marrow plasma cell numbers, but are required for repopulation of plasma cell-deficient bone marrow. Thereby, depleting mature and memory B cells does not have a dramatic negative effect on preexisting Ab levels.

ObjectiveTo identify similarities and differences in the clinical features of adult Japanese patients with individual anti-aminoacyl-tRNA synthetase antibodies (anti-ARS Abs).MethodsThis was a retrospective analysis of 166 adult Japanese patients with anti-ARS Abs detected by immunoprecipitation assays. These patients had visited Kanazawa University Hospital or collaborating medical centers from 2003 to 2009.ResultsAnti-ARS Ab specificity included anti-Jo-1 (36%), anti-EJ (23%), anti-PL-7 (18%), anti-PL-12 (11%), anti-KS (8%), and anti-OJ (5%). These anti-ARS Abs were mutually exclusive, except for one serum Ab that had both anti-PL-7 and PL-12 reactivity. Myositis was closely associated with anti-Jo-1, anti-EJ, and anti-PL-7, while interstitial lung disease (ILD) was correlated with all 6 anti-ARS Abs. Dermatomyositis (DM)-specific skin manifestations (heliotrope rash and Gottron’s sign) were frequently observed in patients with anti-Jo-1, anti-EJ, anti-PL-7, and anti-PL-12. Therefore, most clinical diagnoses were polymyositis or DM for anti-Jo-1, anti-EJ, and anti-PL-7; clinically amyopathic DM or ILD for anti-PL-12; and ILD for anti-KS and anti-OJ. Patients with anti-Jo-1, anti-EJ, and anti-PL-7 developed myositis later if they had ILD alone at the time of disease onset, and most patients with anti-ARS Abs eventually developed ILD if they did not have ILD at disease onset.ConclusionPatients with anti-ARS Abs are relatively homogeneous. However, the distribution and timing of myositis, ILD, and rashes differ among patients with individual anti-ARS Abs. Thus, identification of individual anti-ARS Abs is beneficial to define this rather homogeneous subset and to predict clinical outcomes within the “anti-synthetase syndrome.”

To clarify the association of clinical and prognostic features with dermatomyositis (DM)specific autoantibodies (Abs) in adult Japanese patients with DM.

The presence of anti-MDA5 Ab identifies the characteristic skin, musculoskeletal, pulmonary and prognostic features in patients with DM. In addition, anti-MDA5 Ab seems to predict a group of patients with CADM-complicated fatal RPILD.

Objective. To identify the 140-kd autoantigen recognized by anti-155/140 autoantibodies that are associated with adult cancer-associated dermatomyositis (DM) and juvenile DM and to determine the clinical relevance of anti-155/140 antibodies in a large cohort.Methods. Sera from 456 DM patients were assessed for the presence of anti-155/140 antibodies by immunoprecipitation using K562 cell extracts as substrate. Using immunoprecipitation and Western blotting, we then examined whether anti-155/140-positive sera recognized transcription intermediary factor 1␣ (TIF-1␣), TIF-1␤, and TIF-1␥. The clinical associations of antigen reactivity were also evaluated.Results. Anti-155/140-positive sera reacted with 140-kd TIF-1␣ in addition to 155-kd TIF-1␥. Among sera from 456 DM patients, 52 were reactive with both TIF-1␣ and TIF-1␥, while another 25 were reactive with TIF-1␥ alone. Additionally, 7 were reactive with TIF-1␤. Malignancy was more frequently found in adult patients with both anti-TIF-1␣ and anti-TIF-1␥ antibodies than in those with anti-TIF-1␥ antibodies alone (73% versus 50%; P < 0.05). In addition to juvenile DM patients and middle-aged and older DM patients with high percentages of malignancy, 8 "young adult" DM patients without malignancy had these autoantibodies.Conclusion. Anti-155/140 antibodies target TIF-1 family proteins, TIF-1␣ and TIF-1␤, in addition to TIF-1␥. Since TIF-1 proteins have significant roles in oncogenesis, these antibodies may be produced during misdirected antitumor immunity.Polymyositis (PM) and dermatomyositis (DM) are idiopathic inflammatory disorders that mainly affect the muscle and/or skin (1). Clinical manifestations of PM/DM are heterogeneous, with varying degrees of myositis, skin rash, and accompanying symptoms such as interstitial lung disease and internal malignancy. The association of malignancy with PM/DM, which is termed cancer-associated myositis, is well appreciated, particularly in patients with DM (2-6). Since malignant disease is one of the main causes of mortality in these patients, diagnosing occult cancer in them is important and challenging for clinicians.

This novel MSA is associated with cancer-associated DM and may serve as a diagnostic serological marker for this specific subset.

CD20 monoclonal antibody (mAb) immunotherapy is effective for lymphoma and autoimmune disease. In a mouse model of immunotherapy using mouse anti–mouse CD20 mAbs, the innate monocyte network depletes B cells through immunoglobulin (Ig)G Fc receptor (FcγR)-dependent pathways with a hierarchy of IgG2a/c>IgG1/IgG2b>IgG3. To understand the molecular basis for these CD20 mAb subclass differences, B cell depletion was assessed in mice deficient or blocked for stimulatory FcγRI, FcγRIII, FcγRIV, or FcR common γ chain, or inhibitory FcγRIIB. IgG1 CD20 mAbs induced B cell depletion through preferential, if not exclusive, interactions with low-affinity FcγRIII. IgG2b CD20 mAbs interacted preferentially with intermediate affinity FcγRIV. The potency of IgG2a/c CD20 mAbs resulted from FcγRIV interactions, with potential contributions from high-affinity FcγRI. Regardless, FcγRIV could mediate IgG2a/b/c CD20 mAb–induced depletion in the absence of FcγRI and FcγRIII. In contrast, inhibitory FcγRIIB deficiency significantly increased CD20 mAb–induced B cell depletion by enhancing monocyte function. Although FcγR-dependent pathways regulated B cell depletion from lymphoid tissues, both FcγR-dependent and -independent pathways contributed to mature bone marrow and circulating B cell clearance by CD20 mAbs. Thus, isotype-specific mAb interactions with distinct FcγRs contribute significantly to the effectiveness of CD20 mAbs in vivo, which may have important clinical implications for CD20 and other mAb-based therapies.