Abstract:
In two previously described donors, the extracellular domain of LAIR1, a collagenbinding inhibitory receptor encoded on chromosome 19 (ref. 1), was inserted between the
V and DJ segments of an antibody. This insertion generated, through somatic mutations,
broadly reactive antibodies against RIFINs, a type of variant antigen expressed on the
surface of Plasmodium falciparum-infected erythrocytes. To investigate how frequently
such antibodies are produced in response to malaria infection, we screened plasma from
two large cohorts of individuals living in malaria-endemic regions. Here we report that 5-
10% of malaria-exposed individuals, but none of the European blood donors tested, have
high levels of LAIR1-containing antibodies that dominate the response to infected
erythrocytes without conferring enhanced protection against febrile malaria. By
analysing the antibody-producing B cell clones at the protein, cDNA and gDNA levels,
we characterized additional LAIR1 insertions between the V and DJ segments and
discovered a second insertion modality whereby the LAIR1 exon encoding the
extracellular domain and flanking intronic sequences are inserted into the switch region.
By exon shuffling, this mechanism leads to the production of bispecific antibodies in
which the LAIR1 domain is precisely positioned at the elbow between the VH and CH1
domains. Additionally, in one donor the genomic DNA encoding the VH and CH1
domains was deleted, leading to the production of a camel-like LAIR1-containing
antibody. Sequencing of the switch regions of memory B cells from European blood
donors revealed frequent templated inserts originating from transcribed genes that, in
rare cases, comprised exons with orientations and frames compatible with expression.
These results reveal different modalities of LAIR1 insertion that lead to public and
dominant antibodies against infected erythrocytes and suggest that insertion of templated
DNA represents an additional mechanism of antibody diversification that can be selected
in the immune response against pathogens and exploited for B cell engineering.