Table 2. Amino acid segments and sequence types associated with P. falciparum density in the placenta.
| Segment | Positiona | Sequence type | Consensusb | Mean parasites/μl ×103 (range) | IRR (95% CI) | P c | Median B epitope score (IQR)d |
| DBL2X | |||||||
| S2A | 668–674 | S2A.1 | EYTKxLE | 59.0 (0.2, 213.4) | 4.6 (1.7, 12.5) | 0.003 | 0.1 (−0.3, 0.4) |
| S2A.2 | DFTK(D/N)xE | 12.8 (0.2, 77.1) | ref. | −0.01 (−0.2, 0.3) | |||
| S2B | 772–780 | S2B.1 | EQRQx(K/E)VNA | 88.4 (0.2, 213.4) | 10.7 (3.4, 33.6) | <0.001 | 0.2 (−0.1, 0.4) |
| S2B.2 | KQRQENVNA | 58.6 (0.3, 134.7) | 7.1 (2.6, 19.8) | <0.001 | 0.2 (0.1, 0.5) | ||
| S2B.3 | (E/K)QRQxKVKx | 14.0 (0.2, 7.3) | 1.7 (0.5, 5.6) | 0.383 | 0.3 (0.2, 0.6) | ||
| S2B.4 | (E/K)QRQ(E/A)KVNA | 8.2 (0.2, 134.7) | ref. | 0.1 (0.02, 0.4) | |||
| S2C | 802–803 | S2C.1 | (E/K)CKNK(C/−) | 47.1 (9,2, 202.9) | 27.4 (5.6, 133.7) | <0.001 | 0.3 (0.3, 0.5) |
| S2C.2 | (K/E)C | 44.9 (0.2, 213.4) | 26.1 (8.8, 77.3) | <0.001 | 0.6 (0.6, 0.7) | ||
| S2C.3 | EC(E/K)KKC | 1.7 (0.2, 4.9) | ref. | 0.6 (0.5, 0.6) | |||
| DBL3X | |||||||
| S3A | 1275–1283 | S3A.1 | NLWxK(S/R)Y(G/V) | 62.8 (0.2, 202.9) | 13.8 (4.0, 47.1) | <0.001 | 0.3 (0.01, 0.7) |
| S3A.2 | ELWYK(S/R)Y(G/V) | 48.7 (0.3, 213.4) | 10.7 (3.4, 33.5) | <0.001 | 0.1 (−0.2, 0.4) | ||
| S3A.3 | ELWDKxYG | 4.6 (0.2, 39.2) | ref. | 0.5 (0.2, 0.7) | |||
| S3B | 1324–1332 | S3B.1 | xNx(M/−)(D/−)(K/−)K(G/−) (Q/−)(K/−)x(K/−) | 48.4 (0.3, 213.4) | 12.6 (3.1, 51.5) | <0.001 | 1.5 (0.8, 1.8) |
| S3B.2 | RNPMKEGGEDGKG(K/N)QKEGG | 3.8 (0.2, 67.3) | ref. | 1.9 (1.2, 2.1) | |||
| S3C | 1424–1431 | S3C.1 | xKKQKKxGT | 69.6 (0.5, 213.4) | 6.0 (2.1, 17.5) | 0.001 | 1.3 (0.9, 1.4) |
| S3C.2 | NKKxK(K/E)(N/D)GT | 23.0 (0.3, 134.7) | 2.0 (0.7, 5.8) | 0.214 | 1.3 (0.8, 1.4) | ||
| S3C.3 | xKK(Q/−)(N/D)NK(C/G)T | 11.6 (0.2, 77.2) | ref. | 0.9 (0.8, 1.0) | |||
IRR, incidence rate ratio (i.e., proportional increase in placental parasite density); CI, confidence interval; IQR, interquartile range; ref., reference category.
a
Referred to A4 VAR2CSA.
b
‘x’ indicates positions with 3 or more possible residues, including alignment gaps (see Datasets S1 and S2). Conserved lysine in S3B (K1328 in A4 strain) is underlined.
c
Negative binomial regression with robust estimation of variance.
d
Median of all BepiPred scores for each residue within a sequence type.