Significant increase in antibodies to non-Lyme disease antigens after 28 days is due to the second exposure to the non-Lyme disease.
What is first immune response?
First immune response is the initial reaction of the immune system to invading microorganisms which includes the formation of memory B cells.
That is to say, upon the first exposure of invading antigens such as non-Lyme disease antigens, the body will generate antibodies together with memory cells that will fight against the non-Lyme disease antigen should in case a second exposure occurs.
When a second exposure finally occurs, as seen in the image, the memory B cells already generated in the first exposure would release a high amount of antibodies to fight the non-Lyme disease.