Affinity maturation of anti-lipid IgG antibodies produced via germinal center

Abstract Non-bilayer phospholipid arrangements (NPA) are lipid associations different to the bilayer and are found on cell membranes; they participate in different cellular functions and are transient, but when they are stabilized by drugs such as chlorpromazine, they become immunogenic and induce the formation of anti-NPA antibodies. Mice that receive stabilized NPA share several characteristics with patients with systemic lupus erythematosus, such as the presence of anti-cardiolipin, anti-histone and anti-nuclear antibodies, lupus band, malar exanthema and glomerulonephritis. Mice with this lupus model have been shown to develop the disease as a consequence of the production of anti-NPA antibodies; in addition, most of these antibodies are of the IgG class and are produced mainly by the germinal center pathway. In the case of protein antigens, germinal centers are the sites where class-switch recombination, somatic mutation, memory generation and affinity maturation occur. To determine if affinity maturation, a hallmark of the antibodies produced via germinal center reactions, occurs in the anti-NPA IgG antibodies produced in germinal centers, we performed antigen-specific ELISAs, both in the absence and in the presence of urea. We observed that the percentage of urea-resistant (high affinity) anti-NPA IgG antibodies in relation to the total anti-NPA IgG antibodies increases over time, and it correlates with the number of NPA-specific germinal center B cells.