Recruitment of IgA-producing Plasma Cells into the Mammary Gland

So let me show you how B cells develop or how B cells are differentiate into the IgA producing B cells. These panels are already shown, so let me explain one more time. Before pregnancy, during pregnancy, and during lactation, just after parturition one week after parturition, two weeks after parturition, and then after weaning and then you already learn that two weeks after parturition you can see high number of IgA producing plasma cells and the mammary glands So what we did next is to isolate the cells from the individual mammary gland Then we did a flow cytometric analysis Using 2 markers, one is IgA, the other is B220 Because if you have very naive type B cells that express B220, which is one of B cell marker.

So you can distinguish that the cells are B220 positive, IgA negative. But these cells are activated then differentiate into plasmablast once they are activated by antigens. So after differentiation into the plasma breast, they express both B220 and IgA Then after that, the cells then finally differentiate into plasma cells which express only IgA, not B220. So if you do the flow cytometric analysis using B220 and IgA you can distinguish what type of B cells are present in the mammary gland. So one dot here is one cells, and what if you see the B220 positive, IgA negative which is the upper left region that is mature B cells.

And if you see B220 positive and IgA positive cells that are in upper right region, that is plasmablasts. And if you have IgA positive, B220 negatives plasma cells that are fully differentiated B cells, you can see the cells in the lower right regions. Then you can understand what type of B cells are accumulated in the mammary gland. So let’s compare the tissue image and flow cytometric data especially two weeks after parturition when you find a high number of IgA producing plasma cells.

So in this stage, two weeks after partitions, the most cells are B220 negative and IgA positive, like 41.1%.. Meaning that the fully differentiated IgA producing cells, plasma cells are accumulated in the mammary glands from somewhere

And this is the quantitative number of mature naive B cells and plasma cells that we detected in the mammary gland Again, the number of plasma cells which are fully differentiated IgA producing cells are highly recruited in the mammary gland two weeks after parturition. But mature B cells or plasmablasts are almost undetectable. So these results clearly indicated that actually mammary gland can produce IgA antibodies by recruitment or plasma cells. But the mammary glands are not immune tissues because in the mammary glands the tissues cannot induce B220 differentiation from mature B cells to plasmablasts, to plasma cells Because they need to recruit fully differentiate plasma cells from somewhere.

So we really want to know which, where is the organ which is where is the source of IgA-producing plasma cells that produce maternal IgA antibodies? That is the next experiment.