Among B cell non-Hodgkin's lymphomas, MALT lymphomas express a unique antibody repertoire with frequent rheumatoid factor reactivity

Abstract

We analyzed the structure of antigen receptors of a comprehensive panel of mature B non-Hodgkin's lymphomas (B-NHLs) by comparing, at the amino acid level, their immunoglobulin (Ig)V(H)-CDR3s with CDR3 sequences present in GenBank. Follicular lymphomas, diffuse large B cell lymphomas, Burkitt's lymphomas, and myelomas expressed a CDR3 repertoire comparable to that of normal B cells. Mantle cell lymphomas and B cell chronic lymphocytic leukemias (B-CLLs) expressed clearly restricted albeit different CDR3 repertoires. Lymphomas of mucosa-associated lymphoid tissues (MALTs) were unique as 8 out of 45 (18%) of gastric- and 13 out of 32 (41%) of salivary gland-MALT lymphomas expressed B cell antigen receptors with strong CDR3 homology to rheumatoid factors (RFs). Of note, the RF-CDR3 homology without exception included N-region-encoded residues in the hypermutated IgV(H) genes, indicating that they were stringently selected for reactivity with auto-IgG. By in vitro binding studies with 10 MALT lymphoma-derived antibodies, we showed that seven of these cases, of which four with RF-CDR3 homology, indeed possessed strong RF reactivity. Of one MALT lymphoma, functional proof for selection of subclones with high RF affinity was obtained. Interestingly, RF-CDR3 homology and t(11;18) appeared to be mutually exclusive features and RF-CDR3 homology was not encountered in any of the 19 pulmonary MALT lymphomas studied.

Figure 1.

Schematic representation of the IgV_H clones identified in M41. The lollipop-shaped symbols indicate nucleotide differences as compared with the V1-69 (DP10) germline IgV _H gene. Except for the CDR3 region, replacement and silent mutations are indicated with closed and open circles, respectively, with codon numbering according to V-base indicated underneath. 2×, two mutations in the indicated codon. The mutations in codons 76 and 82a are different between M41-A/B and M41-C, respectively. In the CDR3 and in codon 106, interclonal differences are indicated by different filling patterns of the circles. In the CDR3, the deduced aa sequence is depicted in the one-letter code underneath. The CDR3 of M41-A/D, M41-B and M41-C displayed, respectively, 73, 82, and 91% homology to the CDR3 of RF-WOL. M41-D has only two mutations, shared with M41-A, B, and C.

Figure 2.

IgV_H-CDR3 amino acid sequences of selected cases of MALT lymphoma with homology to IgV_H-CDR3 of rheumatoid factors. MALT lymphomas M5/M6, M11, and M41 share homology with V3-7-RF, V1-69-RF, and WOL-RF, respectively. In addition, RF CDR3 homology of three MALT lymphoma cases from literature (ML27, Iso-3, and ML16) with V3-7-RF, V1-69-RF, and WOL-RF, respectively, is depicted. The amino acid sequences are depicted by the single letter code. FR3 and FR4, framework region 3 and 4; N, amino acids encoded by the nontemplated nucleotides; D, gene segment; JH, gene segment; |, identical amino acids; +, similar amino acids; x, nonmatching amino acids; CDR3 length, length of the CDR3 region; Hom, percentage of homologous amino acids; Id, percentage of identical amino acids; Gap, length difference in amino acids of the compared IgV_H-CDR3 regions.

Figure 3.

RF activity of lymphoma-idiotype-derived antibodies. (a) Titration of IgM LIDAs M5, M6, M9, M11, M21, M22, M41-A, M41-B, FL6'94, B-CLL26, 8D8, and RF control serum in the IgM-RF ELISA. The LIDAs M8, M14, M23, M41-D, FL1, FL8'92, FL13, and LOS3 did not react with human IgG and showed a similar binding curve as that of FL6'94. (b) Binding activity of IgM LIDAs, RF control serum, and anti-Rh(D) control IgM Abs (LOS3 and 8D8) in the IgM-RF ELISA. All samples were tested at a stratified concentration of 500 ng/ml IgM. The ABS 450 nm is plotted without subtraction of the background (BG) ABS 450 nm. (c) IgA-RF ELISA of two serum samples of M22 and as controls an IgA anti-Rh(D) Ab (VT-7G3), an IgA-RF-containing serum, the RF control serum that was also used in the IgM-RF ELISA, and two negative-control serum samples, respectively. All samples were tested at a stratified concentration of 20 μg/ml IgA. The net ABS 450 nm is plotted with subtraction of the background ABS 450 nm.