TABLE 1.

Simultaneous production of IgG1 and IgG3 by B cells with differing malaria antigen specificities^a

Parameter	No. (%) of sera with indicated MSP-119-specific IgG1 OD		No. (%) of sera with indicated AMA-1-specific IgG1 OD
	Less than median	More than median	Less than median	More than median
MSP-2-specific IgG3 with OD < median	341 (35.2)	136 (15.8)	318 (33.4)	162 (17.5)
MSP-2-specific IgG3 with OD > median	120 (14.8)	306 (34.2)	152 (16.5)	296 (32.5)
χ2 value	14.1		13.5
P	<0.001		<0.001

^aIgG1 responses to MSP-1₁₉ or AMA-1 and IgG3 responses to MSP-2 were compared with sera from individual donors. If IgG3 responses to MSP-2 are regulated independently of IgG1 responses to MSP-1₁₉ or AMA-1, then 25% of sera should give ODs above the median for both MSP-2-specific IgG3 and MSP-1₁₉- or AMA-1-specific IgG1. Conversely, if making an IgG1 response to MSP-1₁₉- or AMA-1-specific IgG1 inhibited the simultaneous generation of IgG3 responses to MSP-2, then significantly less than 25% of sera would give ODs above the median for both. The data indicate that IgG1 and IgG3 occur together significantly more often than expected, suggesting that there is no cross-inhibition of IgG1 and IgG3 production.