Fig. 6

Model based on the co-occurrence of J⁺ or J⁻ B cells leading to structurally different IgA1 assemblies in serum and milk. A blood vessel is depicted with antibodies originating from either J⁺ or J⁻ B cells, which expressing either dimeric J-chain coupled IgA1 or monomeric IgA1, respectively. The representation of each J⁺ or J⁻ B cell is depicted in the dashed box in the top left corner. Only the J⁺ B cells expressing dimeric J-chain coupled IgA1s are shared between human serum and milk. These shared IgA1s can enter the serum or mammary epithelial cells by axillary lymph nodes and be picked up by pIgR to be transported from the lamina propria to the lumen where it is expressed as SIgA1