How <i>P</i>. <i>falciparum</i> increases the risk of endemic Burkitt’s lymphoma.

<p>Essentially all adults are persistently infected with EBV (A). As a consequence, newly infected B cells are continually being produced that transit the GC on their way to becoming latently infected memory B cells (the site of viral persistence) [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005331#ppat.1005331.ref014" target="_blank">14</a>]. Malaria is immunosuppressive (B) [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005331#ppat.1005331.ref016" target="_blank">16</a>,<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005331#ppat.1005331.ref017" target="_blank">17</a>], and Torgbor et al. have shown that this results in a highly elevated throughput of EBV-infected cells in the GC (C). Torgbor et al. also showed that <i>P</i>. <i>falciparum</i> induces deregulated expression of the DNA-mutating and -cutting enzyme AID in GC cells (D). Robbiani et al. subsequently showed in a mouse model that this deregulated expression led to DNA damage, translocations, and, ultimately, lymphoma (E). Thus, infection with <i>P</i>. <i>falciparum</i> has been shown to have two effects on the GC, where eBL originates. Together, these increase the risk that a GC cell will undergo a c-myc translocation and that this cell will also be EBV-infected and, therefore, able to tolerate the translocation, synergistically increasing the likelihood that eBL will arise.</p

A Multifactorial Role for <i>P. falciparum</i> Malaria in Endemic Burkitt's Lymphoma Pathogenesis

<div><p>Endemic Burkitt's lymphoma (eBL) arises from the germinal center (GC). It is a common tumor of young children in tropical Africa and its occurrence is closely linked geographically with the incidence of <i>P. falciparum</i> malaria. This association was noted more than 50 years ago. Since then we have learned that eBL contains the oncogenic herpes virus Epstein-Barr virus (EBV) and a defining translocation that activates the c-myc oncogene. However the link to malaria has never been explained. Here we provide evidence for a mechanism arising in the GC to explain this association. Accumulated evidence suggests that eBL arises in the GC when deregulated expression of AID (Activation-induced cytidine deaminase) causes a c-myc translocation in a cell latently infected with Epstein-Barr virus (EBV). Here we show that <i>P. falciparum</i> targets GC B cells via multiple pathways to increase the risk of eBL. 1. It causes deregulated expression of AID, thereby increasing the risk of a c-myc translocation. 2. It increases the number of B cells transiting the GC. 3. It dramatically increases the frequency of these cells that are infected with EBV and therefore protected from c-myc induced apoptosis. We propose that these activities combine synergistically to dramatically increase the incidence of eBL in individuals infected with malaria.</p></div

c-myc is expressed in GC B cells.

<p>A. Flow cytometric analysis demonstrating c-myc expression in tonsil GC cells (CD10+). The arrow indicate the CD10+, c-myc positive GC population. B. Western blot analysis confirming c-myc expression in 3 independent tonsil GC B cell preparation (GC1-3). Raji and Rael are EBV positive BL cell lines. The molecular weight in KD is shown to the left. C. ImageStream analysis of c-myc positive tonsil GC B cells. Staining for a known nuclear protein bcl-6 is shown for comparison. N.B. For this study only Boston control tonsils were used.</p

Hemozoin is taken up by B cells and activates AID expression.

<p>A. Hemozoin (sHz) (red) and CpG (green) were incubated with two different B cell lines. Note presence of red granules inside both cell types. BL2 is an EBV negative BL line and IM171 a spontaneous EBV positive lymphoblastoid line. B. Hemozoin stimulates expression of AID mRNA to an equivalent level to that obtained with surface Ig cross-linking and CpG. The stimulation was independent of hemozoin being complexed with parasite DNA. The same protocol was followed as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1004170#ppat-1004170-g001" target="_blank">Figure 1</a>. The cells were analyzed after a 5 day incubation period.</p

Higher levels of EBV infected cells in tonsil GCs from individuals infected with <i>P. falciparum</i> malaria compared to controls.

<p>A. The percentage of B cells (CD19+) is unchanged. (ns p = 0.18). B. The percentage of GC B cells (CD10+) is significantly elevated in the malaria tonsils (*** p<0.001). C. The frequency of GC B cells latently infected with EBV is dramatically increased in the malaria tonsils (*** p = 0.001). For details see <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1004170#ppat-1004170-t001" target="_blank">Table 1</a>. D. The level of EBV infected GC B cells and AID expression do not directly correlate.</p

<i>P. falciparum</i> extracts stimulate expression of AID protein in normal tonsil B cells.

<p>The same protocol was followed as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1004170#ppat-1004170-g001" target="_blank">Figure 1</a>, except the cells were analyzed by staining for AID protein expression and FACS analysis after a 5 day incubation period. - Flow cytometry histograms of cell populations demonstrate equivalent levels of AID expression in B cells activated by CpG or <i>P. falciparum</i> extracts. MFI  =  Mean fluorescence intensity. A. and C. Percentage of all B cells expressing AID (B) and percent of B cells expressing high levels of AID (C) suggest equal levels of AID expression in B cells activated by CpG or <i>P. falciparum</i> extract. We observed two overlapping populations of cells staining positive for AID. An arbitrary gate imposed on the brighter population defined high level expressers. The same gate was applied to all samples.</p