The authors tested whether MHC dissimilarity and IgH dissimilarity between partners affect sperm viability in two types of secretions of the female reproductive tract in humans, namely follicular fluids and cervical mucus. The viability of sperm was tested in vitro in 2 full-factorial experiments, i.e. testing all of 160 and 144 pair combinations, respectively, and each combination was tested twice. I understand that analyses based on these two experiments have already been published in Jokiniemi et al. 2020a and 2020b where the authors had focused on MHC genetic dissimilarity based on allele identities (like most previous studies on MHC-linked sexual selection). In the present re-analyses, the authors now focus on the immunoglobulin banding regions (eplets) of the MHC molecules, which I think is a good idea and interesting by itself. The authors also newly analyze and discuss possible effects of IgH dissimilarities between the partners. The study is well done, the paper generally well written, and the results are interesting. I have the following comments:

1) State how many men and women participated in both experiments, i.e. were these the same 8 men and the same 9 women, and if not, how many men and how many women participated in both experiments?

2) If these were the same men and women, why could one woman not be included in the experiments with cervical mucus?

3) Related to point 1: if some men and some women were used in both experiments, to what degree are similarities on HLA eplets and IgH correlated? Please discuss if such a correlation is likely, and what it would mean for the conclusions of the present study.

4) The figures only show fitted values as obtained from the LMM. It would be good to also see the non-fitted (raw) observations, for example, in a separate figure or in the Supplementary Materials.

5) It would be useful to see how HLA eplets and HLA genetic dissimilarity are related to each other in the present samples.

6) Line 144: The subtitle does not reveal that this chapter also explains how IgH genotype difference was calculated.

7) Line 252: “be” instead of “by”

The authors have responded appropriately to all my comments. One of their responses now raises a new problem:

The authors now demonstrate that there is a strong and positive correlation between HLA eplet dissimilarity and IgH dissimilarity in the study that focuses on the possible effects of cervical mucus (line 190). This is also the only study where IgH dissimilarity correlates with sperm viability (Table 2). It is therefore possible that the significant effect of IgH dissimilarity is confounded by HLA eplet dissimilarity. Showing that HLA eplet dissimilarity itself does not significantly correlate with sperm velocity in the cervical mucus experiment (Table 1) doesn’t solve the problem yet. The authors would have to find a way to separate the possible effects of IgH dissimilarity from HLA eplet dissimilarity. I believe that in the present case, such a separation could only be done statistically, and my guess is that with this rather small sample size, there is probably not enough statistical power to do so. I therefore find the conclusions that “… both HLA alleles and immunoglobulins may facilitate female choice” (Abstract) and that “… partners’ genetic compatibility may have wider immunological basis than traditionally has been assumed” (final sentence of Abstract) premature. There are analogous premature conclusions in the text that would need to be changed.

Testing for effects of HLA eplet dissimilarity was based on strong a priori predictions (see literature cited in Introduction), while there is no strong a priori prediction on the effects of IgH dissimilarity. I would therefore argue that as long as the effects of IgH dissimilarity and HLA eplet dissimilarity cannot be disentangled, the role of IgH dissimilarity remains unclear. I recommend that the authors are very explicit about this.

Minor comments:
Line 190 “… in the study on effects of cervical mucus” instead of “… in cervical mucus”
Line 190 “… in the study on effects of follicular fluid” instead of “… in follicular fluid”